git annex webapp now opens a browser to the webapp

Also, starts the assistant if it wasn't already running.

Utility/Daemon.hs

@@ -62,24 +62,33 @@ lockPidFile onfailure file = do
 	where
 		newfile = file ++ ".new"
 
-{- Stops the daemon.
+{- Checks if the daemon is running, by checking that the pid file
+ - is locked by the same process that is listed in the pid file.
  -
- - The pid file is used to get the daemon's pid.
- -
- - To guard against a stale pid, check the lock of the pid file,
- - and compare the process that has it locked with the file content.
- -}
-stopDaemon :: FilePath -> IO ()
-stopDaemon pidfile = do
-	fd <- openFd pidfile ReadOnly (Just stdFileMode) defaultFileFlags
-	locked <- getLock fd (ReadLock, AbsoluteSeek, 0, 0)
-	p <- readish <$> readFile pidfile
-	case (locked, p) of
-		(Nothing, _) -> noop
-		(_, Nothing) -> noop
-		(Just (pid, _), Just pid')
-			| pid == pid' -> signalProcess sigTERM pid
-			| otherwise -> error $
+ - If it's running, returns its pid. -}
+checkDaemon :: FilePath -> IO (Maybe ProcessID)
+checkDaemon pidfile = do
+	v <- catchMaybeIO $
+		openFd pidfile ReadOnly (Just stdFileMode) defaultFileFlags
+	case v of
+		Just fd -> do
+			locked <- getLock fd (ReadLock, AbsoluteSeek, 0, 0)
+			p <- readish <$> readFile pidfile
+			return $ check locked p
+		Nothing -> return Nothing
+	where
+		check Nothing _ = Nothing
+		check _ Nothing = Nothing
+		check (Just (pid, _)) (Just pid')
+			| pid == pid' = Just pid
+			| otherwise = error $
 				"stale pid in " ++ pidfile ++ 
 				" (got " ++ show pid' ++ 
 				"; expected" ++ show pid ++ " )"
+
+{- Stops the daemon, safely. -}
+stopDaemon :: FilePath -> IO ()
+stopDaemon pidfile = go =<< checkDaemon pidfile
+	where
+		go Nothing = noop
+		go (Just pid) = signalProcess sigTERM pid