reorder repo parameters last

Many functions took the repo as their first parameter. Changing it
consistently to be the last parameter allows doing some useful things with
currying, that reduce boilerplate.

In particular, g <- gitRepo is almost never needed now, instead
use inRepo to run an IO action in the repo, and fromRepo to get
a value from the repo.

This also provides more opportunities to use monadic and applicative
combinators.

Command/AddUrl.hs

@@ -41,10 +41,9 @@ perform url file = do
 
 download :: String -> FilePath -> CommandPerform
 download url file = do
-	g <- gitRepo
 	showAction $ "downloading " ++ url ++ " "
 	let dummykey = Backend.URL.fromUrl url
-	let tmp = gitAnnexTmpLocation g dummykey
+	tmp <- fromRepo $ gitAnnexTmpLocation dummykey
 	liftIO $ createDirectoryIfMissing True (parentDir tmp)
 	ok <- liftIO $ Url.download url tmp
 	if ok