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.

Command.hs

@@ -187,7 +187,7 @@ filterFiles l = do
 			let regexp = compile (toregex exclude) []
 			return $ filter (notExcluded regexp) l'
 	where
-		notState f = not $ isPrefixOf stateLoc f
+		notState f = not $ isPrefixOf stateDir f
 		notExcluded r f = case match r f [] of
 			Nothing -> True
 			Just _ -> False