Ignore visibility change events when the window is closing (fixes #812).
Merge pull request #833 from openscad/fix-visibility-behavior

Ignore visibility change events when the window is closing (fixes #812).
Disable failing test on Ubuntu 12.04 Gallium drivers
Merge branch 'master' of github.com:openscad/openscad
Merge remote-tracking branch 'origin/master' into test3dexport