improve beauty-fill tool for non-flat triangles.
Project the triangle pair into 2d coords before measuring.

before/after - http://www.graphicall.org/ftp/ideasman42/beauty_fill_fix.png


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54403 954f8c5b-7b00-dc11-b283-0030488c597c