Fixes to Autonav speed.

- Time never slows down unless hostiles are present.
- Actually detects hostile presence, not just enemy presence; in particular, certain hostiles spawned by missions didn't cause time slow-down previously.
- Damage this frame is now required for time to slow down if the slider is below "Enemy Presence".
- When speed resets due to damage, time will not accelerate again for a couple seconds.
- Hostiles aren't considered to be present unless they are nearby for two consecutive frames. This works around a problem where time would reset frequently for one frame, which was annoying.