We're missusing the current frame to pass data from the input subsystem
to the movement prediction without a server frame. While we can use the
current frame for the movements itself, it's not finished and thus
unsuitable for stair step prediction. Also oldframe is determined
wrongly. As a result the player "jumps" over stairs.
This is largely based upon the cl_async 1 mode from KMQuake2, which in
turn is based upon r1q2. The origins of this code may be even older...
Different to KMQuake2 the asynchonous mode is not optional, the client
is always asynchonous. Since we're mainly integrating this rather
fundamental change to simplify the complex internal timing between
client, server and refresh, there's no point in keeping it optional.
The old cl_maxfps cvar controls the network frames. 30 frames should be
enough, even Q3A hasn't more. The new gl_maxfps cvar controls the render
frames. It's set to 95 fps by default to avoid possible remnant of the
famous 125hz bug.
