Triangulate Modifier changes - using scanfill

The ear loop method is potentially too slow (OˆN).

We are not using the 'beauty' option at the moment.
I'll incorporate that next.
(and later specific methods for quad splitting)

Patch done in collaboration (and reviewed by)  with Campbell Barton.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@60618 954f8c5b-7b00-dc11-b283-0030488c597c