remote-hg: redirect buggy mercurial output

Mercurial emits messages like "searching for changes", "no changes
found", etc. meant for the use of its own UI layer, which break the pipe
between transport helper and remote helper.

Since there's no way to silence Mercurial, let's redirect to standard
error.

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

git-remote-hg

@@ -271,6 +271,7 @@ def get_repo(url, alias):
 
     myui = ui.ui()
     myui.setconfig('ui', 'interactive', 'off')
+    myui.fout = sys.stderr
 
     if hg.islocal(url):
         repo = hg.repository(myui, url)