git-p4: use dict.items() iteration for python3 compatibility

git-p4: use dict.items() iteration for python3 compatibility

Python3 uses dict.items() instead of .iteritems() to provide
iteratoration over dict.  Although items() is technically less efficient
for python2.7 (allocates a new list instead of simply iterating), the
amount of data involved is very small and the penalty negligible.

Signed-off-by: Yang Zhao <yang.zhao@skyboxlabs.com>
Reviewed-by: Ben Keene <seraphire@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>