We simply have to disallow any kind of result set being sent back
  from a function. Can't see any way to make that to work.


mysql-test/r/sp-error.result:
  New test case for BUG#8408.
mysql-test/t/sp-error.test:
  New test case for BUG#8408.
sql/item_func.cc:
  Disable result sets from functions but temporarily turning CLIENT_MULTI_RESULTS off.
sql/share/errmsg.txt:
  Added error message for statements not allowed in functions (detected during parsing).
sql/sql_yacc.yy:
  Don't allow result sets in functions.