better directory handling

Rename Locations functions for better consitency, and make their values
more consistent too.

Used </> rather than manually building paths. There are still more places
that manually do so, but are tricky, due to the behavior of </> when
the second FilePath is absolute. So I only changed places where
it obviously was relative.

Version.hs

@@ -29,10 +29,10 @@ getVersion = do
 		then return $ Just v
 		else do
 			-- version 0 was not recorded in .git/config;
-			-- such a repo should have an annexDir but no
-			-- annexObjectDir
-			d <- liftIO $ doesDirectoryExist $ annexDir g
-			o <- liftIO $ doesDirectoryExist $ annexObjectDir g
+			-- such a repo should have an gitAnnexDir but no
+			-- gitAnnexObjectDir
+			d <- liftIO $ doesDirectoryExist $ gitAnnexDir g
+			o <- liftIO $ doesDirectoryExist $ gitAnnexObjectDir g
 			if d && not o
 				then return $ Just "0"
 				else return Nothing -- no version yet