Possible fix for #1701: Contour does not pass a list of linestyles to LineCollection

Conflicts:
	lib/matplotlib/contour.py
Add test for setting dashes for line collections

Conflicts:
	lib/matplotlib/tests/test_lines.py
Add image test for setting line collection dashes
Merge pull request #1718 from dmcdougall/fix_set_dashes

Fix set dashes for line collections