mint-arena: Clear viewport not screen, viewport coords code clean up

Clearing viewport instead of screen will be needed for per-player menus.
mint-arena: Don't use cg.singleCamera for world scene size

Setting cg.singleCamera = qtrue in CG_DrawActiveFrame made global scoreboard draw...
Mecwerks-Logic: fixed stack underflow bug
mint-arena: Fix score info being dropped by server

Server drops reliable command string if it's length is more than 1022.
mint-arena: Don't build score info for bots, they don't parse it
mint-arena: Only fog sky portal if a fog var is specified
Merge remote-tracking branch 'upstream/master'
Mecwerks-Logic: fixed a stupid mistake
Mecwerks-Logic: put accuracy_hits back into weapon_railgun_fire() (suggested by zturtleman)