rhg: Add support for ui.ignore and ui.ignore.* config
This fixes some but not all failures in `tests/test-hgignore.t` when running
with `rhg status` enabled.
Differential Revision: https://phab.mercurial-scm.org/D11907
$ LANG=nonexistent LC_ALL=nonexistent LANGUAGE=nonexistent hg version -q
Mercurial Distributed SCM (version *) (glob)