When beveling two adjacent edges, code used face normal instead
of the face-corner normal (these can be different for nonplanar
faces); the bevel may look uneven in such cases.
Switched to using corner normal, and needed to fix the case
where the edges meet at a reflex angle. Fixed a similar case
when beveling two edges with one non-beveled in between.
Also removed unnecessary argument from offset_meet.
1158c1f7c0