Fix #1991 and #1828.  Integer overlow on Python 3 causes a crash.  Adds a test.
Merge pull request #1991 from mdboom/ticker-overflow

bugfix for matplotlib/ticker.py (python 3.3)
Merge remote-tracking branch 'upstream/v1.2.x'

Conflicts:
	lib/matplotlib/tests/baseline_images/test_axes/formatter_large_small.pdf
	lib/matplotlib/tests/baseline_images/test_axes/formatter_large_small.png