OpenGL error hunt -- dashboard cleanup

Test for context in vtkFrameBufferObject when Get'ing
FBO attributes. This prevents driver segfault in
TestSetGet.tcl on Apple.

Change-Id: If093750770a5a55ac3cd69eaa0a7d8115e2d3771
Merge topic 'opengl-error-hunt' into master

0994d6ca OpenGL error hunt -- dashboard cleanup