Add two 'remove' functions

svn path=/nixpkgs/branches/stdenv-updates/; revision=26311

pkgs/lib/lists.nix

@@ -50,6 +50,11 @@ rec {
   filter = pred: list:
     fold (x: y: if pred x then [x] ++ y else y) [] list;
 
+  # Remove elements 'e' from a list. Useful for buildInputs
+  remove = e: filter (x: x != e);
+
+  # Given two lists, removes all elements of the first list from the second list
+  removeList = l: filter (x: elem x l);
 
   # Return true if `list' has an element `x':
   elem = x: list: fold (a: bs: x == a || bs) false list;