Process penders in the order they're added.
Process penders in the order they're added.

Since this is currently only used to destroy texture and framebuffer handles, it shouldn't really
matter, but it's better to avoid violating expectations just for the fun of it.

This does assume that a stack-blowing number of penders does not accumulate between two frames, but
that is a pretty safe bet.

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