Retrocomputing

This patch resolves a video quality bug in PCSX (and derivatives) and since it is a complete rewrite of the mdec.c file it also allow PCSX to be completely licensed under the GPL.

The rewrite is based on an implementation of the AAN (Y. Arai, T. Agui, and M. Nakajima) IDCT algorithm plus some optimizations based on extra information on the coefficient matrices provided by the RLE decoder.