Check if iterator has length

If an iterable is passed into `FuncAnimation` check if it has
`__len__` before trying to take it's length

closes #1769
added test for code path where the object passed into `frames` is
does not have a length.
corrected test function name
added test_animation back in to default_test_modules so that the
iterator test actually runs
Adds kwarg `which` to Axis.get_ticklabels, Axes.get_xticklabels,
and Axes.get_yticklabels to match the pattern in other tick-related
functions

Closes #1715
Merge pull request #2634 from tacaswell/animation_iter_length

address FuncAnimantion trying to take lengths of generators
Merge pull request #2628 from tacaswell/xticklabels_kwarg

improved get_ticklabels kwarg
Fixed empty text bbox drawing.