python 2/3 support : iteritems and xrange

[ajmirsky]

while python 2.7 is still going to be supported for another 2 years, there are python 3 features that could help in development. most python 3 changes can be made in a backwards compatible way with python 2.7. smaller pull requests focusing on specific classes of changes is probably more approachable; this one focuses on migrating dictionary iteritems and xrange.

for reference:

• http://python-future.org/compatible_idioms.html#iterating-through-dict-keys-values-items
• http://python-future.org/compatible_idioms.html#xrange

ps >> this also includes changes from previous pull request. apologies. in the future, i'll keep these separate.

[ajmirsky]

removed merge conflicts, should be clearer now.