acl: read correct index into url for username (issue298)

The index was inadvertedly off-by-one causing the username to be the
remote host rather than the remote user when hosted in a http(s)
session.

hgext/acl.py

@@ -84,7 +84,7 b' def hook(ui, repo, hooktype, node=None, '
     if source == 'serve' and 'url' in kwargs:
         url = kwargs['url'].split(':')
         if url[0] == 'remote' and url[1].startswith('http'):
-            user = urllib.unquote(url[2])
+            user = urllib.unquote(url[3])
 
     if user is None:
         user = getpass.getuser()