officially dropping support for OSX 10.3 "Panther"

[Graham Percival]

Apparently GUB (from about a year ago) no longer works on 10.3.9.
It's quite possible that this was broken in the change that made it
work on 10.5.

http://code.google.com/p/lilypond/issues/detail?id=1295

I have no clue how to fix the errors.  I'm quite willing to apply test
patches and upload test binaries, but without a dedicated person
working on this, it won't go anywhere.  Unless anybody has a clue,
and/or particularly cares about the operating system that was released
in 2003 and superseded by 10.4 in 2005, I propose that we officially
drop support for 10.3.

Cheers,
- Graham