install a git-annex-shell shim script when the standalone OSX app runs

I put it in ~/.ssh/ because there's no reliable way to get it into PATH,
and OSX ssh doesn't even honor user's PATH by default.

authorized_keys generators will need to check if it's there. Not done yet.

Assistant/Install/AutoStart.hs

@@ -0,0 +1,23 @@
+{- Assistant OSX autostart file installation
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Assistant.Install.AutoStart where
+
+import Utility.OSX
+import Utility.Path
+
+import System.Directory
+
+{- Installs an autostart plist file for OSX. -}
+installAutoStart :: FilePath -> FilePath -> IO ()
+installAutoStart command file = do
+	createDirectoryIfMissing True (parentDir file)
+	writeFile file $ genOSXAutoStartFile autoStartLabel command
+		["assistant", "--autostart"]
+
+autoStartLabel :: String
+autoStartLabel = "com.branchable.git-annex.assistant"