Improved the screen consumer

Improved the screen consumer
============================

* No longer spin waits for vsync (the video card driver seems to do this at
  least with nvidia), but sleeps almost up until the time when the vertical
  blank occurs, thus the time for swap buffers (a smaller spin wait than
  before).
* Now deinterlaces to two separate frames so for example 50i will no longer
  be converted to 25p but instead to 50p for smooth playback of interlaced
  content.

git-svn-id: https://casparcg.svn.sourceforge.net/svnroot/casparcg/server/trunk@3205 362d55ac-95cf-4e76-9f9a-cbaa9c17b72d