- Fix error message to say that "mysql_upgrade" should be run when
 a particular error message is found to be missing
 - Dont's set default value on blob's - it will not be used anyway.


scripts/mysql_system_tables_fix.sql:
  Don't set a DEFAULT value on blob - depending on sql_mode it
  will either be dicarded or throw an error message. But never used.
sql/sql_plugin.cc:
  Update error message to indicate that "mysql_upgrade" should
  be used to correct the problem
sql/sql_udf.cc:
  Update error message to indicate that "mysql_upgrade" should
  be used to correct the problem