real fix for [#35097], (curve cap flipping).

previous commit was incorrect, the face flipping depended on the orientation of the curve.

fix by passing the bevel direction to the fill function so we can have a reliable front/back.

This also gives some speedup for all curve filling since we can avoid calculating the normal since its already known.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56331 954f8c5b-7b00-dc11-b283-0030488c597c