more lock file refactoring

Also fixes a test suite failures introduced in recent commits, where
inAnnexSafe failed in indirect mode, since it tried to open the lock file
ReadWrite. This is why the new checkLocked opens it ReadOnly.

This commit was sponsored by Chad Horohoe.

Remote/Helper/Hooks.hs

@@ -83,18 +83,12 @@ runHooks r starthook stophook a = do
 		unlockFile lck
 #ifndef mingw32_HOST_OS
 		mode <- annexFileMode
-		fd <- liftIO $ noUmask mode $ createLockFile (Just mode) lck
-		v <- liftIO $ tryIO $
-			setLock fd (WriteLock, AbsoluteSeek, 0, 0)
-		case v of
-			Left _ -> noop
-			Right _ -> run stophook
-		liftIO $ closeFd fd
+		v <- liftIO $ noUmask mode $ tryLockExclusive (Just mode) lck
 #else
 		v <- liftIO $ lockExclusive lck
+#endif
 		case v of
 			Nothing -> noop
 			Just lockhandle -> do
 				run stophook
 				liftIO $ dropLock lockhandle
-#endif