* fhandler.cc (fhandler_base::open): Fix typo in comment.

(fhandler_base::close): Move call to del_my_locks from here...
	* fhandler_disk_file.cc (fhandler_disk_file::open): ...to here.
	* flock.cc (struct lockfattr_t): New type.
	(lockf_t::close_lock_obj): New method, use throughout.
	(lockf_t::create_lock_obj_attr): New method.
	(lockf_t::create_lock_obj): Use create_lock_obj_attr method.  Handle
	STATUS_OBJECT_NAME_COLLISION in F_FLOCK case gracefully.  Add lengthy
	comments to explain why and how.
	(lockf_t::open_lock_obj): Use create_lock_obj_attr method.
	(lockf_t::del_lock_obj): Call NtSetEvent rather than SetEvent for
	symmetry.
	(fhandler_disk_file::lock): Define n only where it's used.  Call
	need_fork_fixup only if call was successful.  Handle EINTR and
	ECANCELED return values from lf_setlock.
	(lf_setlock): Drop WAIT_UNLOCKED and WAIT_PROC_EXITED.  Don't wait
	for event object handle count to become <= 1 in F_LOCK case.
	Simplify WFMO return value handling.  Don't handle signal and cancel
	events here; just return with appropriate error code instead.
	(lf_getblock): Ignore locks for which the handle can't be opened.
	Use IsEventSignalled.
	* ntdll.h (STATUS_INVALID_INFO_CLASS): Undef if defined elsewhere to
	make sure the definition is casted to NTSTATUS.
	(STATUS_INVALID_HANDLE): Define and ditto.
	(STATUS_OBJECT_NAME_COLLISION): Define.
	(NtSetEvent): Declare.

winsup/cygwin/fhandler_disk_file.cc

@@ -1380,8 +1380,12 @@ fhandler_disk_file::open (int flags, mode_t mode)
 int
 fhandler_disk_file::close ()
 {
+  /* Close extra pread/pwrite handle, if it exists. */
   if (prw_handle)
     NtClose (prw_handle);
+  /* Delete all POSIX locks on the file.  Delete all flock locks on the
+     file if this is the last reference to this file. */
+  del_my_locks (on_close);
   return fhandler_base::close ();
 }