Bicubic texture upsampling

Added bicubic upsampling and a hybrid mode which uses bicubic in place of bilinear for upsampling the non-XBRZ part of the texture. The texture upscaling stuff is now pretty feature-complete from my point of view. However, there are lots of possible performance improvements -- even on the CPU, and even more so when considering moving the whole thing to the GPU.

I've found that bicubic isn't worth the performance tradeoff in most hardware/software scenarios, but there are some instances (e.g., again, the sky in Wipeout, or huge alpha blended effect sprites) where it's noticeable.