Plug some memory holes.
some small visibility changes.
some small alterations to alien time reservation

don't necessarily reserve TUs for reaction fire if in an "aggro" state
reserve them for moving to cover instead.

(the reasoning behind this will become apparent with the next push)

reaction fire vs aliens is much more common now that they don't reserve
TUs when aggro.
changes to alien fire selection.

aliens will choose various fire modes (as available) according to range,
time units remaining, and time units needed to reach cover.