mint-arena: Fix harvester skull pickup

Both teams could pick up any skull and count toward held skulls.
Picking up your own color skull is suppose to just remove the entitiy.

Caused by commit 8e0cdaf765819b1631398622e84fa27786319b2a.
mint-arena: Fix spawn/freed entity logic (specifically harvester skulls)

- Actually use the second 'force' pass in G_Spawn when out of available slots.
- Make G_EntitiesFree return qtrue if we can open a new slot. (Only used when spawning Harvester skulls.)

Fixes not spawning Harvester skulls when there are no 'open freed slots', but we have other slots available to open.
Merge remote-tracking branch 'mint-arena/master'

Conflicts:
	code/game/g_active.c