this uses a thread to collect vsync input events and filter them
before forwarding them to the mainloop (as a double timestamp). this
means wakeups only happen for the actual vsync and thus animator and
not for other screens we are filtering out anyway. this should fix the
continual animator wakeups that happen if you have a dri/drm based
driver and > 1 screen.
due to mesa changes to hide dri2 symbols, i have had to work on a fix
that makes this work again by going right to drm. now it works and
animators shoudl be vsynced on drm drivers if possible (only 1 card -
use card 0). already existing nvidia solution that uses a lot more
memory is there. others - no support. timers only
this adds a slave process that is useful on nvidia drivers as there
isn't another way to get vsync evenys (that i know about). i need to
make another slave process to that includes a dri2 protocol
implementation since mesa has now hidden its dri2 symbols.