CMake: Require Boost 1.57.0 (fixes Travis OS X)
Clipper: Compact buffers on each clipping pass

Use a new buffer management scheme in the clipper that allows using a
bounded minimal amount of buffer space. Even though it copies more data
it is still slightly faster likely due to using less cache.
Rasterizer: Common sub-expression elimination

Move the computation of some values out of loops so that they're not
constantly recalculated even when they don't change.
GPU: Bitwise texture swizzling

Replace the loop-based texture address swizzling code by a bit-twiddling
implementation, providing a very small speed up. Also simplify
addressing code.
Rasterizer: Pre-divide vertex attributes by W

Execute the division-by-W for perspective-correct interpolation of
values in the clipper, moving them out of the rasterization inner loop.