post-review change - use pointer instead of copy on the stack.
WL#1034 (Internal CRON)
 This patch adds INFORMATION_SCHEMA.EVENTS table with the following format:
  EVENT_CATALOG  - MYSQL_TYPE_STRING  (Always NULL)
  EVENT_SCHEMA   - MYSQL_TYPE_STRING  (the database)
  EVENT_NAME     - MYSQL_TYPE_STRING  (the name)
  DEFINER        - MYSQL_TYPE_STRING  (user@host)
  EVENT_BODY     - MYSQL_TYPE_STRING  (the body from mysql.event)
  EVENT_TYPE     - MYSQL_TYPE_STRING  ("ONE TIME" | "RECURRING")
  EXECUTE_AT     - MYSQL_TYPE_TIMESTAMP (set for "ONE TIME" otherwise NULL)
  INTERVAL_VALUE - MYSQL_TYPE_LONG    (set for RECURRING otherwise NULL)
  INTERVAL_FIELD - MYSQL_TYPE_STRING  (set for RECURRING otherwise NULL)
  SQL_MODE       - MYSQL_TYPE_STRING  (for now NULL)
  STARTS         - MYSQL_TYPE_TIMESTAMP (starts from mysql.event)
  ENDS           - MYSQL_TYPE_TIMESTAMP (ends from mysql.event)
  STATUS         - MYSQL_TYPE_STRING  (ENABLED | DISABLED)
  ON_COMPLETION  - MYSQL_TYPE_STRING  (NOT PRESERVE | PRESERVE)
  CREATED        - MYSQL_TYPE_TIMESTAMP
  LAST_ALTERED   - MYSQL_TYPE_TIMESTAMP
  LAST_EXECUTED  - MYSQL_TYPE_TIMESTAMP
  EVENT_COMMENT  - MYSQL_TYPE_STRING

  SQL_MODE is NULL for now, because the value is still not stored in mysql.event .
Support will be added as a fix for another bug.

 This patch also adds SHOW [FULL] EVENTS [FROM db] [LIKE pattern]
1. SHOW EVENTS shows always only the events on the same user,
   because the PK of mysql.event is (definer, db, name) several 
   users may have event with the same name -> no information disclosure.
2. SHOW FULL EVENTS - shows the events (in the current db as SHOW EVENTS)
   of all users. The user has to have PROCESS privilege, if not then
   SHOW FULL EVENTS behave like SHOW EVENTS.
3. If [FROM db] is specified then this db is considered.
4. Event names can be filtered with LIKE pattern.
  SHOW EVENTS returns table with the following columns, which are subset of
  the data which is returned by SELECT * FROM I_S.EVENTS
   Db
   Name
   Definer 
   Type
   Execute at
   Interval value
   Interval field 
   Starts 
   Ends
   Status


mysql-test/lib/init_db.sql:
  change the PK - (definer, db, name)
  quicker searches when SHOW EVENTS;
  allow also different users to have events with the same name -> 
  no information disclosure
mysql-test/r/events.result:
  result of new tests
mysql-test/r/information_schema.result:
  result of new tests
mysql-test/r/information_schema_db.result:
  result of new tests
mysql-test/r/system_mysql_db.result:
  result of new tests
mysql-test/t/events.test:
  new tests for information_schema.events
scripts/mysql_create_system_tables.sh:
  change the PK of mysql.event to (definer, db, name)
scripts/mysql_fix_privilege_tables.sql:
  change the PK of mysql.event to (definer, db, name)
sql/event.cc:
  pass around the definer of the event because of the new PK
  which is (definer, db, name). It's needed for index searching.
sql/event.h:
  - make enum evex_table_field again public so it can be used
  in sql_show.cc
  - make created and modified ulonglong, because they should be such
  - make public evex_open_event_table so it can be used in sql_show.cc
sql/event_executor.cc:
  - cosmetics
sql/event_priv.h:
  - moved enum evex_table_field and evex_open_event_table()
    to event.h (made them therefore public)
sql/event_timed.cc:
  - in event_timed::init_definer() always fill this.definer with
    the concatenated value of definer_user@definer_host. Makes
    later the work easier.
  - pass around the definer wherever is needed for searching 
    (new prototype of evex_db_find_evex_aux)
sql/mysqld.cc:
  - add counter for SHOW EVENTS
sql/sql_lex.h:
  - register SHOW EVENTS as command
sql/sql_parse.cc:
  - handle SCH_EVENTS (I_S.EVENTS like SCH_TRIGGERS)
  - make additional check in case of SHOW EVENTS (check for EVENT on
    the current database. if it is null check_access() gives appropriate
    message back.
sql/sql_show.cc:
  - add INFORMATION_SCHEMA.EVENTS and SHOW EVENTS
  - I_S.EVENTS.SQL_MODE is NULL for now -> not implemented. Trudy
    asked to be added so bug #16642 can be completely closed. There
    is another bug report which will fix the lack of storage of
    SQL_MODE during event creation.
sql/sql_yacc.yy:
  - always call event_timed::init_definer() when CREATE/ALTER/DROP
    EVENT but not when just compiling the body of the event because
    in this case this operation is not needed, it takes memory and
    CPU time and at the end the result is not used. event_timed::definer
    is used only on SQLCOM_CREATE/ALTER/DROP_EVENT execution not on
    statement compilation.
  - add SHOW [FULL] EVENTS [FROM db] [LIKE pattern]
    in case of FULL and the user has PROCESS privilege then he will see
    also others' events in the current database, otherwise the output
    is the same as of SHOW EVENTS. Because the events are per DB only
    the events from the current database are shown. pattern is applied
    against event name. FROM db is self explanatory.
sql/table.h:
  add SCH_EVENTS as part of INFORMATION_SCHEMA