[Media_api] PortMidi update

[Roger Dannenberg]

Please forgive me for not giving credit to Olivier Trsitan for OS X and
Torgeir Strand Henriksen for Linux patches that are in the latest version.
I'll search some old files and see if I left anyone else out, or send me
email if I did. I don't have a great system for tracking both contributor
names and code changes as things get tested, but I'll try harder. Meanwhile,
I've added names to the changelog in portmidi.h and you should see it online
soon.

-Roger