WL#1218 "Triggers". Some very preliminary version of patch.

Mostly needed for Monty for him getting notion what needed for triggers 
from new .FRM format. 

Things to be done:
- Right placement of trigger's invocations
- Right handling of errors in triggers (including transaction rollback)
- Support for priviliges
- Right handling of DROP/RENAME table (hope that it will be handled automatically
  with merging of .TRG into .FRM file)
- Saving/restoring some information critical for trigger creation and replication
  with their definitions (e.g. sql_mode, creator, ...)
- Replication

Already has some known bugs so probably not for general review.

sql/mysql_priv.h

@@ -471,6 +471,7 @@ int mysql_rm_table_part2_with_lock(THD *thd, TABLE_LIST *tables,
 				   bool log_query);
 int quick_rm_table(enum db_type base,const char *db,
 		   const char *table_name);
+void close_cached_table(THD *thd, TABLE *table);
 bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list);
 bool mysql_change_db(THD *thd,const char *name);
 void mysql_parse(THD *thd,char *inBuf,uint length);
@@ -611,6 +612,7 @@ int mysql_prepare_delete(THD *thd, TABLE_LIST *table_list, Item **conds);
 int mysql_delete(THD *thd, TABLE_LIST *table, COND *conds, SQL_LIST *order,
                  ha_rows rows, ulong options);
 int mysql_truncate(THD *thd, TABLE_LIST *table_list, bool dont_send_ok=0);
+int mysql_create_or_drop_trigger(THD *thd, TABLE_LIST *tables, bool create);
 TABLE *open_ltable(THD *thd, TABLE_LIST *table_list, thr_lock_type update);
 TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT* mem,
 		  bool *refresh);
@@ -637,6 +639,10 @@ Field *find_field_in_table(THD *thd, TABLE_LIST *tables, const char *name,
                            bool check_grant_table,  bool check_grant_view,
 			   bool allow_rowid,
                            uint *cached_field_index_ptr);
+Field *find_field_in_real_table(THD *thd, TABLE *table,
+                                const char *name, uint length,
+                                bool check_grants, bool allow_rowid,
+                                uint *cached_field_index_ptr);
 #ifdef HAVE_OPENSSL
 #include <openssl/des.h>
 struct st_des_keyblock