fix dedicated server timing, now sleeps less than the full amount of time (like liste...

fix dedicated server timing, now sleeps less than the full amount of time (like listen servers/clients already did) to maintain a steady framerate, also made it not sleep unless it is at least 10ms, to try to further improve the timing accuracy, thanks to GreEn`mArine for testing this change

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@5784 d7cf8633-e32d-0410-b094-e92efae38249