WIP: use eglstreams of hybrid systems

I had a little free time thursday, so I thought I'd try to knock out the 3-big-monitors-on-hybrid-nvidia-machines issue (#205), but it ended up consuming most of thursday, friday, monday, and tuesday and I'm still not done 🙂 so I'm just going to post what I got for now and pick it back up later after I do some pending GDM and RHEL work.

it works, but the branch needs quite a bit of clean up and there's bad performance, in part from glReadPixels not being able to use the memcpy fast path. One thing that might be worth experimenting with is texturing straight from the mapped intel buffer object, that way we avoid the read pixels entirely.