test: enable sparse-revlog for test-debugcommands.t
We are about to enable sparse-revlog globally. To help with reviewing the
tests change, we isolate them in individual changesets.
Differential Revision: https://phab.mercurial-scm.org/D5318
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.