Add a helper function for suiciding buildables

Removes duplicate code when suiciding alien and human structures.
Show negative build points even after sudden death

While it's not possible to build after SD, it's possible that buildings
die due to too little BPs.
Add a separate mode of death for no-BP building suicides
Scan if a team has a negative number of build points

The scan occurs periodically in the main loop.

There is a given probability that a building dies within 1 minute if
BP < 0.
Account for build points in the queues

So that buildings don't die when there is enough BPs, but still stuck in
the queue.
Merge pull request #11 from ppetr/negative-bps-1

Negative BPs