Make the travis output slightly quieter, particularly when installing dependencies.  Add Python 3.3 to the tests.
Merge pull request #1965 from mdboom/simplify-travis

Make the travis output quieter on v1.2.x
Update pngsuite.png test image
Fixed failing bbox_inches='tight' case when a contour collection is empty.

Conflicts:
	lib/matplotlib/tests/test_collections.py
SubplotBase._make_twin_axes always creates a new subplot instance. Fixes #1957.
Skip over zero-length subpaths.  Calculate for each subpath and then "or" those results together.
Fix #1973: offset_position == 'data' is not respected by point_in_path_collection
Escape XML comments correctly when writing out SVG.  Turns '--' into '- -'
Merge pull request #1967 from mdboom/svg-comment-escape

svg double hyphen in plot title --
Add a test for #1787
Add test for #1973
Merge pull request #1973 from mdboom/pick_path_collection_data_offset_position

Collection's contains method doesn't honour offset_position attribute
Merge pull request #1787 from mdboom/points_in_path_bug

Path.contains_points() incorrect return
Add a test for #1957
Merge pull request #1972 from mdboom/twin-spine-fix

SubplotBase._make_twin_axes always creates a new subplot instance
Merge remote-tracking branch 'upstream/v1.2.x'

Conflicts:
	.travis.yml
	lib/matplotlib/tests/baseline_images/test_png/pngsuite.png
	lib/matplotlib/tests/test_axes.py