Don't submit quads to the GPU if they won't be drawn

[kalmard0]

Use an early test to determine if a quad will actually fall inside our rendering area. Although the GPU is quick to discard these quads, this is still useful because invalid data won't pollute the UniformQuadBatch buffer and thus reduce the number of draw calls and data copied to the GPU.

[samskivert]

I'm not on board with forcing everyone to incur this expense for every draw call, but I am OK with adding a flag to Surface that turns on intersection testing. I can handle the added expense of a single branch for everyone to make life easier for games that draw a lot of totally invisible images.

[kalmard0]

Great, thank you.
I've seen a performance testbed in version 1 that (I assume) would be great at doing explicit verifications on issues like this. What happened to it?

[samskivert]

It's here:

https://github.com/threerings/playn-perf

I should move it to the playn Github org.