fix alien recovery

- treat the north-west corner of the corpse as the corpse, just as the original did
- reversed some of redv's changes to allow for this, but ran with some good ideas.
- fixed bullet sprite for heavy laser... cause that was bugging me, and i was
already in the ruleset.
- fixed silacoid weapon (it should really have a -1 clipSize)
- fixed points totalling for live aliens that have "accidents"
- fixed reapers
add base defense to "new battle mode"

only using the base defined in the ruleset for the time being, with a view
to opening it up a little, maybe we should add the "custom base" builder
here for some... "thorough testing"