mint-arena: Drop Harvester cubes when entering Team Arena holdable portal

Makes it consistent with using holdable teleporter.
mint-arena: Make Harvester cube drop in a circle when use holdable teleporter

This is done for powerups. Makes dropping many cubes look better, maybe.

Backported from Turtle Arena.
Merge remote-tracking branch 'mint-arena/master'

Conflicts:
	code/game/g_combat.c