VC2005 MMX patch.

Here is the patch with my changes.

Most work went into the decoder. I just changed on the encoder if 
something was nessesary to build the library.

You can find the patch here (quite big)..

    http://torus.untergrund.net/code/theora_mmx_vc2005.diff

Please let me know if the encoder works without problems. I just did a 
very brief testing of it.

The decoder has been tested against the test files from 
http://v2v.cc/~j/theora_testsuite/ . I compared the dumpvid output 
against my version and it looks ok so far.

    Nils