Fix per-triangle intersection for picking.
Fix per-triangle intersection for picking.

A flag for plane vs. triangle intersection was incorrectly inverted
when fixing other bugs with transformations and picking. Flipping it
back fixes per-triangle intersections. Previously, since every
triangle was being tested as a plane, the per-triangle checks would
almost universally pass. Fixes #231.

sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata