Fix for BUG#24923: Functions with ENUM issues.

The problem was that the RETURNS column in the mysql.proc was of
CHAR(64). That was not enough for storing long-named datatypes.

The fix is to change CHAR(64) to LONGBLOB, and to throw warnings
at the time a stored routine is created if some data is truncated
during writing into mysql.proc.

scripts/mysql_system_tables_fix.sql

@@ -344,6 +344,7 @@ ALTER TABLE proc MODIFY name char(64) DEFAULT '' NOT NULL,
                              'MODIFIES_SQL_DATA'
                             ) DEFAULT 'CONTAINS_SQL' NOT NULL,
                  MODIFY body longblob NOT NULL,
+                 MODIFY returns longblob NOT NULL,
                  MODIFY sql_mode
                         set('REAL_AS_FLOAT',
                             'PIPES_AS_CONCAT',