- fixed wrong test case for bug 20903
 - closed the dangling connections in trigger.test
 - GET_LOCK() and RELEASE_LOCK() now produce more detailed log
 - fixed an omission in GET_LOCK() : assign the thread_id when
    acquiring the lock.


mysql-test/r/trigger.result:
  Bug #28992: test case updated
mysql-test/t/trigger.test:
  Bug #28992: test case updated. dangling connections closed.
sql/item_func.cc:
  Bug #28992: 
   - GET_LOCK() and RELEASE_LOCK() now produce more detailed log
   - fixed an omission in GET_LOCK() : assign the thread_id when
      acquiring the lock.