Enable back the disabled test case.


mysql-test/include/mix1.inc:
  Fix a race condition in the test, causing a sporadic failure.
mysql-test/r/innodb_mysql.result:
  Update test case result.
mysql-test/t/disabled.def:
  Enable the test case innodb_mysql.
sql/sql_parse.cc:
  Fix the random failure of innodb_mysql test. The failure is not
  random any more after a patch for Bug 12713 added asserts around
  handler commit.