use ShellParam type

So, I have a type checked safe handling of filenames starting with dashes,
throughout the code.

Content.hs

@@ -60,7 +60,7 @@ logStatus key status = do
 	g <- Annex.gitRepo
 	u <- getUUID g
 	logfile <- liftIO $ logChange g key u status
-	Annex.queue "add" ["--"] logfile
+	Annex.queue "add" [Param "--"] logfile
 
 {- Runs an action, passing it a temporary filename to download,
  - and if the action succeeds, moves the temp file into