- Include kis_opengl.h in order to include gl/glew headers and necessary platform dependent headers. Should hopefully fix build on OS X too.
- Add begin/endOpenGL() methods to KisOpenGLCanvas2 (and convenience methods to KisTool to call them). These save and restore the GL state set by QPainter and should be used to wrap native OpenGL calls, allowing the two systems to work together.
- Change check for shading language extensions to just check for OpenGL 2.0 or greater, as that should be good enough these days.
- Change OpenGLCanvas2 to implement paintEvent() rather than paintGL(), as recommended by Qt's sample. Also split the function into smaller sub-functions.
- Make the GLSL shader and program wrapper classes non-copyable. They were only working as they were due to compiler-dependent behaviour (return value optimisation).

BUG: 220703

svn path=/trunk/koffice/; revision=1070094