Further process tweaks

- Integrates Volundr's btime library and associated process scheduler
changes.
- btime is implemented separately from the process scheduler, as precise
time measurement is also useful elsewhere.
- `TimeOfHour` is no longer internally throttled; throttling is instead
done by `SCHECK`.
- If btime's `gettime` cannot be called at world startup, an error will
be output and the world will stop.
- Retains the change to schedule processes according to game time,
rather than real time.
- Removes the (now unused) update queue files.
- Removes the process scheduler testing files.
- These are standalone tests for the process scheduler, completely
unrelated to its use in the full codebase. We never used them.
- Moves the process scheduler defines into __DEFINES.
- Makes the lighting process run once before the round starts.
- Renames `scheck` to `sleepCheck`, to ensure any code that tries to use
`scheck` will fail to compile.
- Adds `SCHECK` and `SCHECK_EVERY` macros that skip calling `sleepCheck`
entirely until a specified number of `SCHECK`s (50 by default) have been
called.
- Makes most processes iterate using their `last_object` variable,
allowing hang recovery to show the type that caused the hang.
- Makes processes output an error when they filter out a type they
refuse to process.
- Rolls the recently-added alarm subsystem into the alarm process.
- Removes the now unused subsystems code.

code/modules/garbage collection/garbage_collector.dm

@@ -64,7 +64,7 @@ var/global/datum/controller/process/garbage_collector/garbageCollector
 			queue.Cut(1, 2)
 			soft_dels++
 			dels_count++
-		scheck()
+		SCHECK
 
 #ifdef GC_DEBUG
 #undef GC_DEBUG

code/modules/lighting/lighting_process.dm

@@ -3,7 +3,7 @@
 	var/last_overlay_count = 0
 
 /datum/controller/process/lighting/doWork()
-	var/list/lighting_update_lights_old = lighting_update_lights //We use a different list so any additions to the update lists during a delay from scheck() don't cause things to be cut from the list without being updated.
+	var/list/lighting_update_lights_old = lighting_update_lights //We use a different list so any additions to the update lists during a delay from SCHECK don't cause things to be cut from the list without being updated.
 	last_light_count = lighting_update_lights.len
 	lighting_update_lights = null //Nulling it first because of http://www.byond.com/forum/?post=1854520
 	lighting_update_lights = list()
@@ -21,7 +21,7 @@
 		L.force_update = 0
 		L.needs_update = 0
 
-		scheck()
+		SCHECK
 
 	var/list/lighting_update_overlays_old = lighting_update_overlays //Same as above.
 	last_overlay_count = lighting_update_overlays.len
@@ -32,4 +32,4 @@
 		O.update_overlay()
 		O.needs_update = 0
 
-		scheck()
+		SCHECK