Add normlike()
Initial variables in Leg ctor
Add blanks to/from a home position
Fixed background adaptation of bg that disappears
Mark a track as visible only when at least one hit couldn't be a bg pixel
Reduce BGLONGDISTLIFE

From 30s to 10s, since only frames/scans where there is no target are
counted
dbg changes
Added 'a' command to tracker to cycle through apps