Create a special package for the hidden window used to make offscreen pbuffers. Make the hidden window current before destroying pbuffers made with it. Intel graphics fail with pbuffer context on new drivers  https://tracker.physiomeproject.org/show_bug.cgi?id=2693 Merge from cmgui_2_7_0_plus_fixes revision C8029
Create a special package for the hidden window used to make offscreen pbuffers.
Make the hidden window current before destroying pbuffers made with it.
Intel graphics fail with pbuffer context on new drivers 
https://tracker.physiomeproject.org/show_bug.cgi?id=2693
Merge from cmgui_2_7_0_plus_fixes revision C8029


git-svn-id: 4705079bc6b8aadf675e3696f5c015a6aa4916e3@8094 3c1deb5b-d424-0410-962d-aba41a686d42

hsorby/zinc,OpenCMISS/zinc,OpenCMISS/zinc,OpenCMISS/zinc,hsorby/zinc,hsorby/zinc,hsorby/zinc,OpenCMISS/zinc