* fhandler.h (enum del_lock_called_from): New enumeration.

	* fhandler.h (enum del_lock_called_from): New enumeration.
	(fhandler_base::del_my_locks): Declare taking a del_lock_called_from
	as argument.
	* fhandler.cc (fhandler_base::close): Call del_my_locks with "on_close".
	(fhandler_base::fixup_after_fork): Call del_my_locks with "after_fork".
	(fhandler_base::fixup_after_exec): Call del_my_locks with "after_exec".
	* flock.cc (fhandler_base::del_my_locks): Take del_lock_called_from
	as argument.  Call node->del_my_locks with NULL handle in after_exec
	case.  Explain why.