-protect open() against being called from different threads simultaniously,
 we are then thread safe except for the jpeg decompression under the following
 assumption:
 * We assume all device setup (for a single device) is done from a single
   thread
 * We assume that at the time an videodev fd gets closed all other threads
   which may have been using it have stopped using it.

-add support for setting / getting the number of read buffers

-add code to v4l2_read to not return frames more then say 5 seconds old

-add support for libv4l1 for non pure capture (combined capture and overlay)
 devices so that atleast CGMBUF emulation (but no conversion, as thats
 impossible for overlays) can be done, so that it will no longer be
 necessary to implement CGMBUF in the kernel for each driver.

-add (configurable) support for alsa faking enum_fmt to libv4l2 ?

-check v4l2_field during conversion

-add make install target

-add conversion from bgr24 to yuv420

-add v4l2_dup, make re-entrant safe (for gstreamer v4l2 support)