acl: make sure the extensions is enabled when the acl-hooks run

The acl extension is usually setup through hooks and never directly activated.
This means the config item declared in the extension are not loaded.
We add the necessary logic to make sure the extensions are loaded before the hook
run.

hgext/acl.py

@@ -198,6 +198,7 b' import getpass'
 from mercurial.i18n import _
 from mercurial import (
     error,
+    extensions,
     match,
     registrar,
     util,
@@ -307,7 +308,23 b' def buildmatch(ui, repo, user, key):'
         return match.match(repo.root, '', pats)
     return util.never
 
+def ensureenabled(ui):
+    """make sure the extension is enabled when used as hook
+
+    When acl is used through hooks, the extension is never formally loaded and
+    enabled. This has some side effect, for example the config declaration is
+    never loaded. This function ensure the extension is enabled when running
+    hooks.
+    """
+    if 'acl' in ui._knownconfig:
+        return
+    ui.setconfig('extensions', 'acl', '', source='internal')
+    extensions.loadall(ui, ['acl'])
+
 def hook(ui, repo, hooktype, node=None, source=None, **kwargs):
+
+    ensureenabled(ui)
+
     if hooktype not in ['pretxnchangegroup', 'pretxncommit']:
         raise error.Abort(_('config error - hook type "%s" cannot stop '
                            'incoming changesets nor commits') % hooktype)