py3: add a r'' prefix in mercurial/exchange.py
# skip-blame because just r'' prefix
This fixes test-narrow-acl.t on py3 which was broken by one of the
earlier patches.
Differential Revision: https://phab.mercurial-scm.org/D5149
py3: add 5 new passing tests to whitelist caught by buildbot
Thanks to everyone who is putting efforts in making hg py3 compatible.
Differential Revision: https://phab.mercurial-scm.org/D5148