Fix crashes related to transports

Fixes two specific causes of transport related crashes, one prevents
infantry from continuing to take damage by Tiberium if loaded into the
transport over Tiberium, and one fixes the edge case where an infantry
dies in the same tick cycle as it was loaded into the transport.
Minor style nit fix

Minor style nit fix
Merge pull request #5324 from Squiggles211/apc_load_crash

Fixes #4790
Fixes #5270
separate content install from loadscreen
unify install from CD logic
unify music install and add a download option

closes #4759
fix Tiberian Dawn CD rip logic

closes #4424