patchbomb: make `hg email` reusable for other patch sources
Adds two internal options, patches and patchnames, which allow other extensions
to email a given set of patches. The pbranch extension needs this to send its
patches which are diffs between topic branches.
To run the tests, do:
cd tests/
python run-tests.py
See http://www.selenic.com/mercurial/wiki/index.cgi/WritingTests for
more information on writing tests.