Merge branch 'jbolz_pipeline_barrier_fixes' into 'master'

Merge branch 'jbolz_pipeline_barrier_fixes' into 'master'

pipeline_barrier fixes

- Try to use the full (power of two) buffer size. Not doing so tickles several issues to do with not writing all bytes of the buffer or image.
- Fix FillBuffer::verify byte selection.
- Use R8G8 rather than R8G8B8 for the vertex format. The third component is out of bounds for the last vertex, which makes the entire attribute undefined (i.e. substituted with zero on some implementations).
- Subtract out epsilon in vertex shader math to avoid points on the frustum boundary which may be culled.

See merge request !227