subrepo: use repo['.'] instead of repo['']...
subrepo: use repo['.'] instead of repo['']
The "state" value (a revision) passed to abstractsubrepo.phase() can
be '' to represent the currently checked out revisions. Let's convert
that to the more common '.'.
I think this is the last of use of repo['.'] in core.
Differential Revision:
https://phab.mercurial-scm.org/D3019
