and tried to do it properly this time, digging out all show commands that
  need the multi results flag set.


mysql-test/r/sp.result:
  New test case for BUG#4902, with lots of other show commands as well.
mysql-test/t/sp.test:
  New test case for BUG#4902, with lots of other show commands as well.
sql/sp_head.cc:
  The check for possible multiple result commands was becomming unwieldly,
  so we moved it to a separate function, and added loads of new command codes
  to the test.
sql/sp_head.h:
  The check for possible multiple result commands was becomming unwieldly,
  so we moved it to a separate function.
sql/sql_yacc.yy:
  The check for possible multiple result commands was becomming unwieldly,
  so we moved it to a separate function.