uhhh, actually, we *want* allocations from 'calloc'.
switch shader to OpenGL ES 3.0.

Even old Mesa 9.2 supports it, so it's likely to be widely
supported.
gfx: set needed GL version to 3.1, from 3.2.

Looks like we don't actually need anything from .2, so might as
well set it lower... plus this is the version my laptop exports.
fix up debug message
gl: the program must be 'used' before we can grab uniforms.