RendererBloom will abort if there aren't 7 texture units available.

Will cleanly fall back to fixed function rendering
Removes attempt to render error messages.

Just spit them out in a message box, instead.  Much easier.
(TODO:  Implement on OSX and Linux)

Adds ability to set 'error context', for extra debugging information.
Need to think about that a bit, whether there's a nicer way to do this.
Not really ready for prime time usage, yet.