wx backend should not attempt to render jpeg/tiff if PIL is present.

If PIL is present, the wx backend needs to allow the base class to get the
job done for print_jpeg and print_tiff, instead of trying to take over
duties itself.
Fix #1999: dash value of zero causes infinite loop
Fixed hatch clipping.
Merge pull request #1999 from mdboom/dashes-infinite-loop

Setting dashes to (0,0) results in infinite loop for agg backends
Don't overwrite unit_circle vertices -- causes problems for many other tests
Merge pull request #6 from mdboom/hatch_clipping_v1.2.x

Don't overwrite unit_circle vertices in clipping test
Merge pull request #2003 from pelson/hatch_clipping_v1.2.x

Fixed hatch clipping.
Fix #2016: reading memory past the end of a C++ std::vector
Merge pull request #2016 from mdboom/ttconv-crash

Crash when using character with umlaut
Merge remote-tracking branch 'upstream/v1.2.x'

Conflicts:
	lib/matplotlib/backend_bases.py
	lib/matplotlib/tests/test_artist.py
	src/_backend_agg.cpp