Add a request capture function

[greggman]

I'd like to add a request capture function. Sometimes I'd like to capture the first or second frame but as it is I can only click the capture button and pray.

It's also useful for debugging because you can put a call the capture in some sample and compare old to new at exactly the same state.

Any preference for how to add it? You've got the "GLI_frame_terminator" extension. I could just add it to that. It's just got a funny name. I could make a new extension "GLI_frame_capture" or I could combine them and rename it like "GLI_helper_api" or something like that.

Thoughts?