For Darwin, code expects SDL_mixer to be in the framework path.
Use that here too.
Add search SDL_mixer framework paths for headers instead of using <Framework/Header.h> notation
Merge commit 'osx-fixes' into unification/master

SDL on OS X does not include pkg-config files, so assume the user put it
in the OS X specific "framework" directory.

Reported by btb: https://github.com/dxx-rebirth/dxx-rebirth/issues/14
Requested by btb: https://github.com/dxx-rebirth/dxx-rebirth/issues/15
Search for SDL_mixer pkg-config too

Users might install SDL and SDL_mixer to separate paths, so search for
SDL_mixer.pc too.
reenable int3
don't know why int3 would be here
add project
add scons args
Move XCode project to contrib/
point project to main dir, rename target
check for GM_MULTI before trying to do network jobs
use relative path for build dir
delete references to old projects
no opengl for now
Merge branch 'xcode' of github.com:btb/dxx-rebirth into xcode

Conflicts:
	contrib/dxx-rebirth.xcodeproj/project.pbxproj