libart: transforming SVPs

[chrismail gnwy100 wuh wustl edu]

Once again, I can answer my own question.  It may not make much sense to
transform an SVP because it won't be sorted after an arbitrary transform.  I
will just convert it back to an ArtVpath and do the transformation there.

However, this may point out the potential usefulness of an
art_vpath_vpath_stroke(..) call (unless I'm still confused).  Maybe I'll work on
that.

(Wow, this list is really helpful in making me realize my own stupidity :)

-chris