Can't test EXT_debug_label, as that is apparently OSX 10.9-only. Added
GL tests for all implemented objects. KHR_debug is selected first, if
that is not available, fall back to EXT_debug_label. If neither is
available, the functions are no-op.
I hope EXT_debug_label gets replaced by KHR_debug later, thus it is now
only "emulated" through KHR_debug enums.
Renamed AbstractShaderProgram::maxSupportedVertexAttributeCount() to
maxVertexAttributes(), the old function is now an alias to retain
source compatibility, will be removed in future release.
Also printing the values in magnum-info.
Robust *Framebuffer::read() access, ability to query robust buffer
access behavior in Context::flags(), ability to check graphics reset
status and reset notification policy in Renderer.
Magnum.h now doesn't include anything except OpenGL headers, thus
changes in Math library don't trigger recompilation of everything, but
only of things really depending on it.
Math constants moved to separate file for similar reasons, de-inlined
some functions to remove the need for some #includes.
AbstractImporter now provides access to the data directly and doesn't
attempt to do any OpenGL stuff, thus making everything more transparent
and testable.