Checking OpenGL extensions causes crash on OS X

This issue was created automatically from an original Mantis Issue. Further discussion may take place here.

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Some python tests crash on OS X. This is due to the fact that OpenGL extensions are being queried before a context was created. The culprit is:

if ( this->HasVolumePipeline ) { // Shouldn't this check be on the render server? vtkHAVSVolumeMapper* mapper = vtkHAVSVolumeMapper::New(); if (mapper && mapper->SupportedByHardware()) { this->SupportsHAVSMapper = 1; }

There are 2 problems with this:

1. If SetInputInternal() is called before a render window is created on the client, this crashes on some platforms
2. The extensions should really be checked on the render server (and maybe on the client as well) not just the client