acl: use configlist to retrieve the source config

This is what the previous code was about.

hgext/acl.py

@@ -219,7 +219,7 b" configitem('acl', 'config',"
     default=None,
 )
 configitem('acl', 'sources',
-    default='serve',
+    default=['serve'],
 )
 
 def _getusers(ui, group):
@@ -292,7 +292,7 b' def hook(ui, repo, hooktype, node=None, '
         raise error.Abort(_('config error - hook type "%s" cannot stop '
                            'incoming changesets nor commits') % hooktype)
     if (hooktype == 'pretxnchangegroup' and
-        source not in ui.config('acl', 'sources').split()):
+        source not in ui.configlist('acl', 'sources')):
         ui.debug('acl: changes have source "%s" - skipping\n' % source)
         return