mysql-test/r/sp.result:
  New test case for BUG#9004.
  Also updated some other results, since formerly "invisible" (but correct)
  warnings now are visible.
mysql-test/t/sp.test:
  New test case for BUG#9004.
sql/sql_error.cc:
  Don't reset warnings while executing a stored routine.
sql/sql_parse.cc:
  Don't reset warnings while executing a stored routine.