small fix for visual glitch in graphs
make it a boolean.

change the kneel function to return a true/false value,
and use it to avoid an infinite loop in the walk state.
aggro difficulty will always be correct
AI fixes

- fix for psychic aliens shooting through walls
- fix for unitSpotted calculation
hyper detected UFOs stay hyper detected.
whoops.
fix turning/walking
fix strafe
Merge pull request #391 from hmaon/ai_fixups

survey function now uses Vol's new voxel exposure function
Linux is case-sensitive
re-run FOV *after* aliens get set non-visible

not before