largefiles: add support for 'largefiles://' url scheme
This changesets allows Mercurial to transparently download content from the
configured largefile store. This handle all authentication and largefile
protocol details.
The target usecase is to leverage largefile infrastructure for clone bundle. See
next changeset for details
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.