Added check in autoscale_None for completely masked pcolor plots.
Add What's new entries for 1.3.1
Python3 handling of None > None.
Merge pull request #2336 from pelson/completely_masked

Added check in autoscale_None for completely masked pcolor plots.
Merge remote-tracking branch 'upstream/v1.2.x' into v1.3.x

Conflicts:
	lib/matplotlib/tests/test_colors.py