Make ResInsight buildable on MacOS X

With these changes, ResInsight can be *built* using Apple Xcode 4.6.3 on MacOS X 10.8.4. Some of these changes may be beneficial for building with Clang on Linux as well.

Although the resulting application will launch it is not yet functional, *probably* because the use of shaders require an OpenGL 3.2 profile but this is somewhat incompatible with GLEW . I haven't looked too closely into that (yet).