py3: use dict.items() instead of dict.iteritems() in tests
dict.iteritems() is not present in Python 3.
Differential Revision: https://phab.mercurial-scm.org/D2353
py3: add b'' prefixes in fakedirstatewritetime.py
# skip-blame because we are just adding b''
Differential Revision: https://phab.mercurial-scm.org/D2350