tests/helper-runtests.sh

manifest: define and implement rev() on manifestlog

Various code is accessing repo.manifestlog._revlog - a private
attribute. This bypasses our interface and makes it difficult to
implement non-revlog manifest storage.

This commit adds a rev() method to the manifestlog interface and
class and teaches callers to use it.

Ideally this method wouldn't exist, as very few consumers should
need to resolve the revision number of a manifest. Again, the
primary goal of interface work is to establish and use interfaces
first and to improve them later.

Differential Revision: https://phab.mercurial-scm.org/D3882

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL