Multiple changes

- Backporting and minor fixups in the Spectra advanced example.
- Fixed build problems with the Spectra example on Windows.
- Updated the multithreading-related classes used in the examples.
Added GL version detection to the build system
Multiple changes

- Minor updates in the GL version and extensions detection modules of the build system.
- Added GL version requirements to some of the examples.
- Updated the tools.
Added an example update in the GLUT harness

- Added a simple example showing the usage with GLSL 120.
- Updated the GLUT example harness to disable primitive queries
  if they are not supported.
Added a new example showing usage with GLSL 120
Minor fixup in one of the examples
Added a new example (showing usage with GLSL 120).
Fixup in the build system
Merge branch 'develop' into feature-oalplus
Update of the build/testing system

- Reimplemented the build system for tests and test fixtures
  in the same way the building of examples and example harnesses
  is done.
- Added a test case that tests if all configured examples compile
  and link properly.
- Minor update in the configure.py script; with the --build option
  "cmake --build path/to/build/dir" is used as fallback command
  to build the examples, textures, etc.
Merge branch 'develop' into feature-oalplus