Merge pull request #495 from esc24/izip_extra_aux_coords

Removal of strict constraint in izip().
PP save with no time forecast.
Merge pull request #498 from bjlittle/pp_save_time

PP save with no time forecast.
Make tests optional that depend on pydot and pandas (optional installs).
Merge pull request #479 from pp-mo/options_tests

Make tests optional that depend on pydot and pandas (optional installs).
 New pp rule to calculate forecast period.