Rollback the multitexturing for the moment.

Things are less stellar in real-world applications; there's a cost
to the multitexturing, but it's outweighed by the gain from reducing
flushes. But if you're managing to do lots and lots of quads using the
same texture, no such gain.

I'm digging into ways to reduce the cost, but so far the best looking
option is waiting until playn can really use opengl es 3.0 because that
adds functionality to properly handle this instead of jumping through
flaming hoops like this. Damnit.

This DOES keep the splitting out from a5d3813, though. That change
definitely makes it much easier for custom shader to do moderate color
twiddling without so much copy & paste.