py3: call branchmap.items() on py3 and continue to call iteritems() on py2
Mercurial's source transformer also replaces the 'def iteritems(' in
branchmap by 'def items(', so we need to call whichever version is
there.
#require test-repo pyflakes
Copied from Mercurial core (60ee2593a270)
$ cd "`dirname "$TESTDIR"`"
run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)
$ hg locate -I 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
> | xargs pyflakes 2>/dev/null