Mac OS X 10.3.9/10.4.x support

[alex-free]

I ported SDL 2.0.3 to Mac OS X 10.3.9 last year, and now I've gotten the latest IOQuake3 running once again on Mac OS X 10.3.9/10.4.x. I added my https://github.com/alex-free/panther_sdl2 includes and libs in the same way that the current mac os x ones are. I also created a -DLEGACY_GL flag that switches the default OpenGL renderer to OpenGL1 since OpenGL 2.0 does not exist on PowerPC Mac OS X 10.3.9 or 10.4.x (was introduced in Leopard, and even there only a few PowerPC Macs support OpenGL 2.0). The resulting app and executables were tested to work on Mac OS X 10.3.9, 10.4.11, and 10.5.8 between 2 of my PowerPC Macs.

Bugs:

1. If running on Mac OS X 10.3.9 or 10.4.x, the cross hairs/mouse cursor may freeze in the window when first starting ioquake3.app. The fix is to change the resolution.
2. No SDL joystick support when building for Panther.

Also, I updated the outdated instructions in the readme. The 10.2.8, 10.3.9, and 10.4u SDKs were not being used at all in the current build system.

[alex-free]

Anyone interested in merging this? I am going to do Intel aupport eventually for the same OS versions.

[tomkidd]

I'm interested, yeah, I just got deep into another project and haven't looked at this in a while.

I think what you've got here is probably right or at least close to the right way to integrate something like this.

In any event, yeah, I'll look at it closer as soon as I can. Thanks.

[NuclearMonster]

This PR will not be merged.