server: increase bounding box radius (makes ghosting a little bit nicer)
server: make server-side ghosting feature a bit nicer

The code was checking the cg_ghost cvar on every server frame. This is
absolutely non needed thus I placed the check in SV_UpdateUserinfo_f
qcommon: updated Info_SetValueForKey and Info_SetValueForKey_Big

Will return the length of the infostring the if it exceeded the buffer,
-1 if we got illegal chars in it, otherwise 0
server: added rcon forcecvar command: force a client userinfo CVAR to a specific value