[Gtkradiant] Mac OS source merged into Alpha branch

[Timothee Besset]

I just commited a merge of the Mac OS branch into the Alpha branch. The
changes are not very important, mostly a few new files and some #ifdef
__linux__ replaced by #if defined(__linux) || defined(__APPLE__)

The original MacOS source is in the MacOS branch, and now Alpha has:
Radiant 1.1-TA reference source + spog's recent changes (patch LOD) +
MacOS patches

I think that Alpha should be the branch to work on for Mac developers
towards next release. Spog's recent changes may not have been
thouroughly tested, but what's in the MacOS branch was branched from
Alpha several months ago and lacks a LOT of the fixes we made towards
1.1-TA release.

Next, I am going to merge the content of Alpha back in the trunk. This
might take a while though.

TTimo