Blender Git Loki

Freestyle: Fix for round/square stroke caps causing line thinning.

This is a regression introduced in rBce729677db3e and rBb408d8af31c9.

RoundCapShader and SquareCapsShader had to remove (almost) overlapping
stroke vertices to avoid sudden thinning of line thickness. For instance,
the test .blend file from https://developer.blender.org/T36425#231460
suffered from the reported line thinning (although T36425 was originally
caused by a different bug).