[Gtkradiant] Mac OS X Port

[EvilTypeGuy]

As you can see from the below screenshot:

http://home.attbi.com/~manownsj00/rr/rr2.jpg

GtkRadiant now builds and runs under XDarwin on Mac OS X. ydnar will be
fixing the endian issues in q3map* at which time there is currently no
known problems beyond. There are currently issues with accelerated
OpenGL under XDarwin but "gparker" one of the main people involved in
XDarwin has expressed a strong interest in ensuring that GtkRadiant
works under XDarwin properly.

All of plugins/ and contrib/ builds perfectly except for md3model and
milkshape 3d model support in the picomodel library due to a bug in how
#pragma pack is handled using the gcc 3.1 compiler that Apple provides.

However, the editor does run, and maps load and save.

I've really only done the "finishing" work on this port, much of the
necessary work had already been done by those who did the initial Linux
port. I had some help from several others along the way too.

Thanks to 'tigital' and 'X-Man' for their assistance of being guinea
pigs for builds since I do not own a Mac OS X box.

Ydnar and TTimo as usual were also of great help.

I believe that as soon as q3map is cinched up, and a possible workaround
is found for the #pragma pack that the apple branch is ready to merged
back into stable.

A side benefit of this porting work is a few small cleanups in radiant
that should help multi-platform support and the bitmap file loader used
for toolbar graphics, etc. is now endian safe.

-eviltypeguy