add visual indicators for suffocation damage

[Vitatroll]

My res is a bit too tiny to tell a difference in sprites beyond 'That guy looks like hamburger' anyways.

I just use examine-results and reason to ascertain health status of slow moving hamburger people. To me that's not really the point, though. Someone slowly turning blue as they rack up suffocation damage is just, as Arborinus stated, 'a very "space station 13 thing"'.