FIX crash when deleting ways

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6429 8aca7d54-2c30-db11-9de9-000461428c89
Fix for "ghost convoi" crash bug after emergency depot teleportation.  Make all versions of depot arrival behave consistently.  Make backup convoi-destruction for stuck convois which cannot be teleported to depot.
Cleanup in setting of aktuell after adding depot to schedule.
Fix places which call emergency_go_to_depot to account for possible convoi destruction.
Fix very important bug where the active player's depot moves would have spacing_shift set to 1 rather than having show_failure set to true !
Remove variable shadowing which may be harming attempts to go to depot
Fix bug where ships at sea would not go to a depot which was also a docking location for a dock.
Add a routine for a depot to check its own suitability against a vehicle.
simconvoi.cc: Add double-checks that we're entering a suitable depot before entering a depot.
Const correctness for new method in simdepot.h
Remove dead code in gui/components/gui_convoy_assembler.cc
simconvoi.cc::laden_abschliessen : delete dead code and use emergency_go_to_depot to avoid duplicated code paths
Fix typo in simdepot.h
Move depot_t::is_suitable_for out of header file, into .cc file; fix it so it works
Really fix is_suitable_for so it works.
CHANGE: Make the forcing of station coverage for factories to be at least 3 limited to saved games with the current, not next version.
FIX: Compile error (but further compile errors remain)
CHANGE: Do not force the factory station coverage size to be at least 3 on the latest save version.
Rewrite convoi_t::go_to_depot and fix all known bugs in go_to_depot.  Tested.
Fix idiot typo bug in assert (sorry, James)