(svn r13687) [0.6] -Backport from trunk:
- Fix: Signals were not updated correctly when a player removed a non-existing track piece (r13626)
- Fix: Signal states could be propagated through waypoints built in orthogonal axis (r13589)
- Fix: Track was not removed on company bankrupcy when there was a ship on lower halftile (r13488)
- Fix: Let ships also navigate on half-tile sloped watery rail tiles (r13485)