Workaround a bug in Intel graphics.
Workaround a bug in Intel graphics.

In IndexedTrisShaders, if we do the various attribute binding up in
activate(), Intel cards give broken behavior. To reproduce it, add three
layers:
 1) An ImageLayer from a CanvasImage (alternately use a SurfaceLayer)
 2) An ImageLayer from an assets-sourced Image
 3) Another ImageLayer from the same assets-sourced Image (subimages count)

Layers 2 & 3 wind up with Layer 1's geometry. If you only do layers 1 & 2,
everything's fine. If it's not a CanvasImage nor SurfaceLayer in position 1,
everything's fine. Very strange.

But we can just do the bind at the last possible chance instead of the first
possible, and everything's fine.

ruslansennov/playn,threerings/playn,ruslansennov/playn,threerings/playn,threerings/playn,threerings/playn,ruslansennov/playn