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/parse_file.h

@@ -27,7 +27,8 @@ enum file_opt_type {
   FILE_OPTIONS_REV,		/* Revision version number (ulonglong) */
   FILE_OPTIONS_TIMESTAMP,	/* timestamp (LEX_STRING have to be
 				   allocated with length 20 (19+1) */
-  FILE_OPTIONS_STRLIST		/* list of strings (List<char*>) */
+  FILE_OPTIONS_STRLIST          /* list of escaped strings
+                                   (List<LEX_STRING>) */
 };
 
 struct File_option