unannex: Clean up use of git commit -a.

This was more complex than would be expected. unannex has to use git commit -a
since it's removing files from git; git commit filelist won't do.

Allow commands to be added to the Git queue that have no associated files,
and run such commands once.

Command/Fix.hs

@@ -44,5 +44,5 @@ perform file link = do
 
 cleanup :: FilePath -> CommandCleanup
 cleanup file = do
-	AnnexQueue.add "add" [Param "--"] file
+	AnnexQueue.add "add" [Param "--"] [file]
 	return True