tests/helper-runtests.sh

revlog: introduce an explicit NodeMap class for pure code

This class make the "pure" nodemap raise the same exception than the C-extension
one.

This is a step toward unifying nodemap and index, the class is not meant to
survive on the long run.

This work is part of a refactoring to unify the revlog index and the nodemap.
This unification prepare the use of a persistent nodemap.

There is a new `isinstance` call, it will be cleaned up in coming changesets.

Differential Revision: https://phab.mercurial-scm.org/D7312

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL