Without SmokeDelay in its Engine section a diesel smokes as soon as the
starter turns, as before; the delay is set per locomotive in its own .fiz.
The value stays a member of the vehicle's mover, read from its .fiz with
an explicit default of 0.
Tests: the real SM42 and ST44 with SmokeDelay=2 and 5 in the .fiz, and
without it (smoke at once), next to a locomotive with a delay loaded
just before, which keeps its own value.
The smoke of a diesel came out at full strength the moment its ignition
set Mains and started the spin up, together with the ignition sound, whose
first part is the starter cranking the engine.
The ignition now starts a countdown of the new optional .fiz parameter
SmokeDelay (Engine section of DieselEngine and DieselElectric vehicles,
seconds, default 2.0, 0 restores the old behaviour); the smoke source of
the vehicle spawns nothing until it runs out. Engines already running, or
switched on another way, smoke as before. No SVN data change is needed;
vehicle authors may tune SmokeDelay to the cranking part of their
ignition: sample.
The spawn count of the smoke source of a vehicle moves out of
smoke_source::update() into smoke::vehicle_spawn_count() (vehicle/smoke.h),
a free function on the mover state, which joins the core library so the
unit tests can call it the way the source does. The rates are the same as
before, the steady rate of the source still counted in before the share of
the engine.
Tests: tests/unit/test_smoke.cpp. A vehicle taken off the tracks spawns no
smoke and drops the pending particles, with the engine starting, idling or
under load; a road vehicle back from the pool puffs again; the engine adds
to the steady rate; the pending count stays within the room of the source.
Two of the four fail without the fix.
Checked again on td.scn with the SM42 driven into a portal: the smoke
source keeps puffing on the run and drops to 0 particles once the vehicle
is taken off the tracks.
