When disk is full, server may waiting for free space while
writing binlog, relay-log or MyISAM tables. The server will 
continue after user have freed some space. But the error
message printed was not quite clear about the how often the
error message is printed, and there will be a delay before
the server continue and user freeing space. And caused users
thinking that the server was hanging forever.

This patch fixed the problem by making the error messages
printed more clear. The error message is split into two part,
the first part will only be printed once, and the second part
will be printed very 10 times.

Message first part:
Disk is full writing '<filename>' (Errcode: <errorno>). Waiting
for someone to free space... (Expect up to 60 secs delay for 
server to continue after freeing disk space)

Message second part:
Retry in 60 secs, Message reprinted in 600 secs

                          
When using mixed mode the record values stored inside the storage
engine differed from the ones computed from the row event. This
happened because the prepare_record function was calling
empty_record macro causing some don't care bits to be left set.
                          
Replacing the empty_record plus explicitly setting defaults with 
restore_record to restore the record default values fixes this.                          

Some changes that make things more elegant in 6.0,
backported so the code is mostly the same in 5.1,
for easier maintainence.

sql/set_var.cc:
  Backporting some changes to 5.1 so the code is
  mostly the same in both versions. Less to learn!

This is a back port from 5.1 to 5.0.

Fix for BUG 20023: mysql_change_user() resets the value
of SQL_BIG_SELECTS.
  
The bug was that SQL_BIG_SELECTS was not properly set
in COM_CHANGE_USER.
  
The fix is to update SQL_BIG_SELECTS properly.



sql/sql_class.cc:
  Update THD::options with the respect to SQL_BIG_SELECTS
  in COM_CHANGE_USER.
tests/mysql_client_test.c:
  Add a test case BUG#20023.

      
When binlog_format is STATEMENT and the statement is unsafe before,
the unsafe warning/error message was issued without checking
whether the SQL_LOG_BIN was turned on or not.
      
Fixed with adding a sql_log_bin_toplevel flag in THD to check
whether SQL_LOG_BIN is ON in current session whatever the current is in sp or not.


mysql-test/suite/binlog/r/binlog_unsafe.result:
  Test case result for unsafe warning/error message
mysql-test/suite/binlog/t/binlog_unsafe.test:
  Test case for unsafe message warning/error
sql/set_var.cc:
  Adding a function set_option_log_bin_bit() which specailly handles to
  the change of SQL_LOG_BIN bit in order to set sql_log_bin_toplevel
  according to SQL_LOG_BIN current value at the same time.
sql/sql_class.cc:
  Initialize the flag sql_log_bin_toplevel in THD::init(),
  and add the condition to check whether unsafe ror message was issued.
sql/sql_class.h:
  Add a sql_log_bin_toplevel flag in THD to indicate whether the toplevel SQL_LOG_BIN is

set user variable max length on
fix_length_and_dec() stage
using real value length.


mysql-test/r/variables.result:
  test result
mysql-test/t/variables.test:
  test case
sql/item_func.cc:
  set user variable max length on
  fix_length_and_dec() stage
  using real value length.

The problem was that the server was trying to use the unknown
error format string (ER_UNKNOWN_ERROR) to print messages about
comments being too long, but the said format string does not
accept arguments and will always default to "Unknown error".

The solution is to introduce new error messages which are
specific to the error conditions so that server wants to
signal -- this also means that it's possible to translate
those messages.

mysql-test/r/strict.result:
  Update test case result.
mysql-test/t/strict.test:
  Update test case with new errors.
sql/share/errmsg.txt:
  Introduce new errors for long comments.
sql/unireg.cc:
  Use new errors.

An unnecessarily restrictive lock were taken on sub-SELECTs during DELETE.

During parsing, a global structure is reused for sub-SELECTs and the attribute
keeping track of lock options were not reset properly.
This patch introduces a new attribute to keep track on the syntactical lock
option elements found in a sub-SELECT and then sets the lock options accordingly.

Now the sub-SELECTs will try to acquire a READ lock if possible
instead of a WRITE lock as inherited from the outer DELETE statement.


mysql-test/r/lock.result:
  Added test case for bug39843
mysql-test/t/lock.test:
  Added test case for bug39843
sql/sql_lex.cc:
  * Reset member variable lock_option on each new query.
sql/sql_lex.h:
  * Introduced new member variable 'lock_option' which is keeping track
    of the syntactical lock option of a (sub-)select query.
sql/sql_parse.cc:
  * Wrote comments to functions.
sql/sql_yacc.yy:
  * Introduced an attribute to keep track of syntactical lock options
    in sub-selects.
  * Made sure that the default value TL_READ_DEFAULT is at the begining
    of each subselect-rule.

remove 'unsigned', 'zerofill' attributes
from DATA_TYPE column value.


mysql-test/suite/funcs_1/r/is_columns_innodb.result:
  result fix
mysql-test/suite/funcs_1/r/is_columns_memory.result:
  result fix
mysql-test/suite/funcs_1/r/is_columns_myisam.result:
  result fix
sql/sql_show.cc:
  remove 'unsigned', 'zerofill' attributes 
  from DATA_TYPE column value.

            
The query cache module did not check for the SQL_NO_CACHE keyword before
attempting to query the hash lookup table. This had a small performance impact.

By introducing a check on the query string before obtaining the hash mutex
we can gain some performance if the SQL_NO_CACHE directive is used often.


sql/sql_cache.cc:
  * Introduced new helper function, has_no_cache_directive, for checking the
    existance of a SQL_NO_CACHE directive before actual parsing of the query.

Backporting patch to 5.0.

      
The problem here seem to be that when mysql
is redirecting stderr to a file, stderr becomes 
buffered, whereas it is unbuffered by definition.

The solution is to unbuffer it by setting buffer
to null.

sql/log.cc:
  use setbuf(stderr, NULL) to set the buffer to null.
sql/mysqld.cc:
  use setbuf(stderr, NULL) to set the buffer to null.

of system errnos when opening a table are masked 
as ER_FILE_NOT_FOUND. This patch handles this as
"Operation failed" as well.

pushbuild".

Under new MTR the server is not restarted for every test, so
threads started in the previous test case can show up in the
results of SHOW PROCESSLIST statement in this test, causing a
test failure.

Since we are not really interested in results of SHOW PROCESSLIST
in this test but rather in fact that server doesn't crash when
executing this statement this fix simply disables output of this
statement.

mysql-test/r/skip_name_resolve.result:
  Disable SHOW PROCESSLIST output to make test immune to threads
  started in previous test cases.
mysql-test/t/skip_name_resolve.test:
  Disable SHOW PROCESSLIST output to make test immune to threads
  started in previous test cases.

This problem comes while inserting a duplicate row in merge table 
without key but the child table has a primary key. 
While forming the error message handler tries to locate the key field
which is creating this problem but as there is no key on the merge
table there is a segmentation fault.

mysql-test/r/merge.result:
  Updated results with new test for this bug.
mysql-test/t/merge.test:
  Added new test to test error generated from a key on child table 
  where merge table doesn't have any key.
storage/myisammrg/ha_myisammrg.cc:
  Added a new check to see if the value of error key is higher than 
  the number of key in merge table and if it is the error key set 
  to MAX_KEY. The error message generation routine treats MAX_KEY as 
  unknown key and doesn't tries to access this in key_info.