Adjust item bit allocations:
* Increase cond flags from 2 bits to 3 bits, for future expansion.
* Use 2 bits remaining in adjacent gap for an auxiliary type field.
This is used for the type (station, waypoint, etc.) of order tests.
Perform a linear scan of the program pool when deleting a station,
waypoint or depot.
This is a port of the tracerestrict/routing restrictions feature
from TTDPatch.
At present this implements if tests (train length only),
and pathfinder deny and penalty actions.
This requires the use of YAPF. Note that restrictions are only evaluated
within the YAPF lookahead distance.
