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
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.