OS X and OpenGL 3.2 support related changes

I made OGLplus build with OS bundled OpenGL and GLUT libraries, not extra dependencies required. I added a couple of ifdefs in the code to make it build with OpenGL 3.2 headers. Along the way I noticed that many examples have their OpenGL version requirement set incorrectly, or not set at all. I corrected some of them.

Before I tried to build it with GLEW, which provides its own GL definitions and it didn't require any changes in the header files. It had everything defined up to version 4.2. But it's dangerous, since it compiles well, but will later crash at runtime. OS X only implements OpenGL 3.2.