moved the code that applies slowmo to demo playback so that it reacts

moved the code that applies slowmo to demo playback so that it reacts
immediately to changes, not at the next packet read (which may never
come if slowmo was set to 0 at any point)
made pausedemo command freeze demo playback in a way that time does not
advance, preventing the problem where it fast forwards to catch up with
where it would have been if not paused after unpausing the demo

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@7306 d7cf8633-e32d-0410-b094-e92efae38249