Do not hardcode qmake executable, it should be found by the CMake itself.
Find the include directory for libunwind.h.

This allows finding libunwind that has been installed in a non-standard location
just by setting CMAKE_PREFIX_PATH.
Fix some missing libraries.
Make building of OpenGL tests and samples optional.
Merge branch 'master' of https://github.com/stativ/vogl into stativ-master

Conflicts:
	src/vogleditor/CMakeLists.txt