Fix #1810: Fix vertical text alignment in the Cairo and OS-X backends.
The renderer backends' draw_text method is now passed the location of
the text baseline, not the bottom of the text bounding box.
Use np.deg2rad instead
Updating all mathtext baseline images to hopefully help Travis pass
Increase image comparison tolerance
Increase tolerance on some more tests
Merge pull request #1810 from mdboom/text-baseline-api

Cairo + plot_date = misaligned x-axis labels