This prevenits the worlds from advancing during client connect. The
player won't get attacked by monsters or hurt by the environment. Note
that in baseq2 there're still 4 world frames processed by the game and
100 world frames if the player enters a level that he or she already
visited. Both aren't a big problem, 4 world frames are hardly enough
for monsters starting to attack and in most levels the starting area
can't be reached by monsters and is free from environmental effects.
Pause mode is only entered for local servers and only in single player
mode. This should prevent problems with coop and deathmatch games.
The behaviour can be controlled by `cl_loadpaused`:
* `0`: Do not enter pause mode, Vanilla Quake I behaviour.
* `1`: Enter pause mode at load and leave it at first regular server
frame.
* `2`: Enter pause mode at load, never leave it. The player must leave
it by hand.
This was requested in issue #417.
cvar operations are special commands that allow the programmatic
manipulation of cvar values. 'reset' resets a given cvar to it's
default value, e.g. `reset r_mode' would reset `r_mode` to `4`.
'resetall' resets all known cvar with the exception of `game`.
The code is based upon q2pro.
This is part of issue #414.
