acl: cleanup module docstring
- removed implementation detail about how the group information is
obtained
- fixed some language, better consistency
- fixed bad comment in hgrc example
% setup
adding a
new tip: 553596fad57b
% test that new changesets are visible to repo.lookup()
new tip: 799ae3599e0e
changeset: 1:799ae3599e0e
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: one more commit to demonstrate the bug