and collateral changes.

* introduce my_hrtime_t, my_timediff_t, and conversion macros
* inroduce TIME_RESULT, but it can only be returned from Item::cmp_type(),
  never from Item::result_type()
* pack_time/unpack_time function for "packed" representation of
  MYSQL_TIME in a longlong that can be compared
* ADDTIME()/SUBTIME()/+- INTERVAL now work with TIME values
* numbers aren't quoted in EXPLAIN EXTENDED
* new column I_S.COLUMNS.DATETIME_PRECISION
* date/time values are compares to anything as date/time, not as strings or numbers.
* old timestamp(X) is no longer supported
* MYSQL_TIME to string conversion functions take precision as an argument
* unified the warnings from Field_timestamp/datetime/time/date/newdate store methods
* Field_timestamp_hires, Field_datetime_hires, Field_time_hires
* Field_temporal
* Lazy_string class to pass a value (string, number, time) polymorphically down the stack
* make_truncated_value_warning and Field::set_datetime_warning use Lazy_string as an argument, removed char*/int/double variants
* removed Field::can_be_compared_as_longlong(). Use Field::cmp_type() == INT_RESULT instead
* introduced Item::cmp_result() instead of Item::is_datetime() and Item::result_as_longlong()
* in many cases date/time types are treated like other types, not as special cases
* greatly simplified Arg_comparator (regarding date/time/year code)
* SEC_TO_TIME is real function, not integer.
* microsecond precision in NOW, CURTIME, etc
* Item_temporal. All items derived from it only provide get_date, but no val* methods
* replication of NOW(6)
* Protocol::store(time) now takes the precision as an argument
* @@TIMESTAMP is a double

client/mysqlbinlog.cc:
  remove unneded casts
include/my_sys.h:
  introduce my_hrtime_t, my_timediff_t, and conversion macros
include/my_time.h:
  pack_time/unpack_time, etc.
  convenience functions to work with MYSQL_TIME::second_part
libmysql/libmysql.c:
  str_to_time() is gone. str_to_datetime() does it now.
  my_TIME_to_str() takes the precision as an argument
mysql-test/include/ps_conv.inc:
  time is not equal to datetime anymore
mysql-test/r/distinct.result:
  a test for an old MySQL bug
mysql-test/r/explain.result:
  numbers aren't quoted in EXPLAIN EXTENDED
mysql-test/r/func_default.result:
  numbers aren't quoted in EXPLAIN EXTENDED
mysql-test/r/func_sapdb.result:
  when decimals=NOT_FIXED_DEC it means "not fixed" indeed
mysql-test/r/func_test.result:
  numbers aren't quoted in EXPLAIN EXTENDED
mysql-test/r/func_time.result:
  ADDTIME()/SUBTIME()/+- INTERVAL now work with TIME values
mysql-test/r/having.result:
  numbers aren't quoted in EXPLAIN EXTENDED
mysql-test/r/information_schema.result:
  new column I_S.COLUMNS.DATETIME_PRECISION
mysql-test/r/join_outer.result:
  numbers aren't quoted in EXPLAIN EXTENDED
mysql-test/r/metadata.result:
  TIMESTAMP no longer has zerofill flag
mysql-test/r/range.result:
  invalid datetime is not compared with as a string
mysql-test/r/select.result:
  NO_ZERO_IN_DATE, etc only affect storage - according to the manual
  numbers aren't quoted in EXPLAIN EXTENDED
mysql-test/r/subselect.result:
  numbers aren't quoted in EXPLAIN EXTENDED
mysql-test/r/sysdate_is_now.result:
  when decimals=NOT_FIXED_DEC it means "not fixed" indeed
mysql-test/r/type_blob.result:
  TIMESTAMP(N) is not deprecated
mysql-test/r/type_timestamp.result:
  old TIMESTAMP(X) semantics is not supported anymore
mysql-test/r/union.result:
  numbers aren't quoted in EXPLAIN EXTENDED
mysql-test/r/varbinary.result:
  numbers aren't quoted in EXPLAIN EXTENDED
mysql-test/t/distinct.test:
  test for an old MySQL bug
mysql-test/t/func_time.test:
  +- INTERVAL now works with TIME values
mysql-test/t/select.test:
  typo
mysql-test/t/subselect.test:
  only one error per statement, please
mysql-test/t/system_mysql_db_fix40123.test:
  old timestamp(X) is no longer supported
mysql-test/t/system_mysql_db_fix50030.test:
  old timestamp(X) is no longer supported
mysql-test/t/system_mysql_db_fix50117.test:
  old timestamp(X) is no longer supported
mysql-test/t/type_blob.test:
  old timestamp(X) is no longer supported
mysql-test/t/type_timestamp.test:
  old timestamp(X) is no longer supported
mysys/my_getsystime.c:
  functions to get the time with microsecond precision
mysys/my_init.c:
  move the my_getsystime.c initialization code to my_getsystime.c
mysys/my_static.c:
  no need to make these variables extern
mysys/my_static.h:
  no need to make these variables extern
scripts/mysql_system_tables.sql:
  old timestamp(X) is no longer supported
scripts/mysql_system_tables_fix.sql:
  old timestamp(X) is no longer supported
scripts/mysqlhotcopy.sh:
  old timestamp(X) is no longer supported
sql-common/my_time.c:
  * call str_to_time from str_to_datetime, as appropriate
  * date/time to string conversions take precision as an argument
  * number_to_time()
  * TIME_to_double()
  * pack_time() and unpack_time()
sql/event_data_objects.cc:
  cast is not needed
  my_datetime_to_str() takes precision as an argument
sql/event_db_repository.cc:
  avoid dangerous downcast (because the pointer is
  not always Field_timestamp, see events_1.test)
sql/event_queue.cc:
  avoid silly double-work for cond_wait
  (having an endpoint of wait, subtract the current time to get the timeout,
  and use set_timespec() macro to fill in struct timespec, by adding the current
  time to the timeout)
sql/field.cc:
  * remove virtual Field::get_time(), everyone should use only Field::get_date()
  * remove lots of #ifdef WORDS_BIGENDIAN
  * unified the warnings from Field_timestamp/datetime/time/date/newdate store methods
  * Field_timestamp_hires, Field_datetime_hires, Field_time_hires
  * Field_temporal
  * make_truncated_value_warning and Field::set_datetime_warning use Lazy_string as an argument, removed char*/int/double variants
sql/field.h:
  * remove virtual Field::get_time(), everyone should use only Field::get_date()
  * remove lots of #ifdef WORDS_BIGENDIAN
  * unified the warnings from Field_timestamp/datetime/time/date/newdate store methods
  * Field_timestamp_hires, Field_datetime_hires, Field_time_hires
  * Field_temporal
  * make_truncated_value_warning and Field::set_datetime_warning use Lazy_string as an argument, removed char*/int/double variants
  * removed Field::can_be_compared_as_longlong(). Use Field::cmp_type() == INT_RESULT instead
sql/filesort.cc:
  TIME_RESULT, cmp_time()
sql/item.cc:
  * numbers aren't quoted in EXPLAIN EXTENDED
  * Item::cmp_result() instead of Item::is_datetime() and Item::result_as_longlong()
  * virtual Item::get_time() is gone
  * Item_param::field_type() is set correctly
  * Item_datetime, for a datetime constant
  * time to anything is compared as a time
  * Item_cache::print() prints the value is available
  * bug fixed in Item_cache_int::val_str()
sql/item.h:
  * Item::print_value(), to be used from Item_xxx::print() when needed
  * Item::cmp_result() instead of Item::is_datetime() and Item::result_as_longlong()
  * virtual Item::get_time() is gone
  * Item_datetime, for a datetime constant
  * better default for cast_to_int_type()
  * Item_cache objects now *always* have the field_type() set
sql/item_cmpfunc.cc:
  * get_year_value, get_time_value are gone. get_datetime_value does it all
  * get_value_a_func, get_value_b_func are gone
  * can_compare_as_dates() is gone too, TIME_RESULT is used instead
  * cmp_type() instead or result_type() when doing a comparison
  * compare_datetime and compate_e_datetime in the comparator_matrix, is_nulls_eq is gone
  * Item::cmp_result() instead of Item::is_datetime() and Item::result_as_longlong()
sql/item_cmpfunc.h:
  greatly simplified Arg_comparator
sql/item_create.cc:
  * fix a bug in error messages in CAST
sql/item_func.cc:
  Item::cmp_result() instead of Item::is_datetime() and Item::result_as_longlong()
  mention all possibitiles in switch over Item_result values, or use default:
sql/item_row.h:
  overwrite the default cmp_type() for Item_row,
  as no MYSQL_TYPE_xxx value corresponds to ROW_RESULT
sql/item_timefunc.cc:
  rewrite make_datetime to support precision argument
  SEC_TO_TIME is real function, not integer.
  many functions that returned temporal values had duplicate code in val_* methods,
  some of them did not have get_date() which resulted in unnecessary date->str->date conversions. 
  Now they all are derived from Item_temporal_func and *only* provide get_date, not val* methods.
  many fixes to set decimals (datetime precision) correctly.
sql/item_timefunc.h:
  SEC_TO_TIME is real function, not integer.
  many functions that returned temporal values had duplicate code in val_* methods,
  some of them did not have get_date() which resulted in unnecessary date->str->date conversions. 
  Now they all are derived from Item_temporal_func and *only* provide get_date, not val* methods.
  many fixes to set decimals (datetime precision) correctly.
sql/log_event.cc:
  replication of NOW(6)
sql/log_event.h:
  replication of NOW(6)
sql/mysql_priv.h:
  Lazy_string class to pass a value (string, number, time) polymorphically down the stack.
  make_truncated_value_warning() that uses it.
sql/mysqld.cc:
  datetime in Arg_comparator::comparator_matrix
sql/opt_range.cc:
  cleanup: don't disable warnings before calling save_in_field_no_warnings()
sql/protocol.cc:
  Protocol::store(time) now takes the precision as an argument
sql/protocol.h:
  Protocol::store(time) now takes the precision as an argument
sql/rpl_rli.cc:
  small cleanup
sql/set_var.cc:
  SET TIMESTAMP=double
sql/set_var.h:
  @@TIMESTAMP is a double
sql/share/errmsg.txt:
  precision and scale are unsigned
sql/slave.cc:
  replication of NOW(6)
sql/sp_head.cc:
  cleanup
sql/sql_class.cc:
  support for NOW(6)
sql/sql_class.h:
  support for NOW(6)
sql/sql_insert.cc:
  support for NOW(6)
sql/sql_select.cc:
  use item->cmp_type().
  move a comment where it belongs
sql/sql_show.cc:
  new column I_S.COLUMNS.DATETIME_PRECISION
sql/sql_yacc.yy:
  TIME(X), DATETIME(X), cast, NOW(X), CURTIME(X), etc
sql/time.cc:
  fix date_add_interval() to support MYSQL_TIMESTAMP_TIME argument
storage/myisam/ha_myisam.cc:
  TIMESTAMP no longer carries ZEROFIELD flag, still we keep MYI file compatible.
strings/my_vsnprintf.c:
  warnings
tests/mysql_client_test.c:
  old timestamp(X) does not work anymore
  datetime is no longer equal to time