blind enabling gcrypt repos on rsync.net

This pulls off quite a nice trick: When given a path on rsync.net, it
determines if it is an encrypted git repository that the user has
the key to decrypt, and merges with it. This is works even when
the local repository had no idea that the gcrypt remote exists!

(As previously done with local drives.)

This commit sponsored by Pedro Côrte-Real

Git/Config.hs

@@ -168,3 +168,12 @@ fromPipe r cmd params = try $
   where
 	p = proc cmd $ toCommand params
 
+{- Reads git config from a specified file and returns the repo populated
+ - with the configuration. -}
+fromFile :: Repo -> FilePath -> IO (Either SomeException (Repo, String))
+fromFile r f = fromPipe r "git"
+	[ Param "config"
+	, Param "--file"
+	, File f
+	, Param "--list"
+	]