ENH: use an artist's update() method instead of the setp() function

The artist.setp() function is a Matlab-compatible function intended
for interactive use.  Its extensive capabilities are not needed
in places like Patch.__init__, where the much faster Artist.update()
method suffices.
Merge pull request #2291 from efiring/no_setp

ENH: use an artist's update() method instead of the setp() function