subrepo: be more careful with deletions of .hgsub and .hgsubstate (
issue2844)
We shouldn't try to process subrepos if .hgsub isn't present and we
should remove .hgsubstate if .hgsub is marked for removal.
To run the tests, do:
cd tests/
python run-tests.py
See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.