Cross-cutting event bits for trap door and task state.

Bit	Meaning
0	Room / script event raised (set by helpers such as Script_Shared_SetEventBit)
1	Trap door is open / trap door event armed
2	Falling-entity latch (cleared/set by Process_Falling_Entities)
3	Object has been offered to the trap (Bad Tempered Thing path)
4	Task-two / upstairs event latch
5	Reserved / unused in the observed call sites
6	Special put-down / room-transition event
7	Task entity script is active