Further update wrt preparation for Timetable mode.
Various improvements in Deadlock processing and alternative path selection.
Slight change in operation of Level Crossings.
Changes in Sky.cs and MSTSSky.cs to avoid errors when starting activity just before midnight.
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@2140 a9f3cfff-6c41-7446-b0ca-052bd761e6eb