Allow both linestyle definition "accents" and dash-patterns as linestyle...

... for collection, lines and patches.

(code & tests)

see. #2136

This is a minimal patch. It seems to me that the linestyle handling could get some more cleanup.
e.g. in lines.py the drawing is handed over to some `_draw_xxx` methods, those are almost only stubs changing the name of the linestyle
That does make a tremendous about of sense to have the line style that means don't draw evaluate to false.

Historically we have had small API breaks on 1.X releases, particularly when they affect things that should not be part of the public API and do have protocol for deprecating APIs.  My point is not that this is a show stopper, just that we need to be a thoughtful about it and make sure to document it.