remote-hg: small performance improvement

Load previous manifest first as Mercurial does; for caching reasons.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/remote-helpers/git-remote-hg

@@ -230,8 +230,9 @@ def get_filechanges(repo, ctx, parent):
     added = set()
     removed = set()
 
-    cur = ctx.manifest()
+    # load earliest manifest first for caching reasons
     prev = repo[parent].manifest().copy()
+    cur = ctx.manifest()
 
     for fn in cur:
         if fn in prev: