Ability to turn changeset public on grfreeze

Created originally on Bitbucket by marmoute (Pierre-Yves David)

Recording draft changeset id in .hgguestrepo is dangerous. Draft changeset may be rewritten an disappear from the repo, leaving a .

I'm considering adding a --publish flags on grfreeze that would turn all referenced changeset public.

I'll send a patch if people agree it is usefull