py3: use list() to get a list of items using dict.items()
dict.items() on Python 3 returns a generator over the values of the dictionary,
hence we can't delete elements while iterating over dict.items() in Python 3.
Differential Revision: https://phab.mercurial-scm.org/D1799
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.