More progress.

- AMBUSH flag on nodes makes them blind and untargetable when getting `startnode` and `goalnode` for `FindPath()`. This is useful for indicating a node should be skipped when tele/portaling, so the current path can be preserved.
- Setup is simple: place nodes behind lines that tele/portal entities and mark them as AMBUSH.

Other changes:

- Restored global array since blockmap is not a viable option here.
- Added MAPINFO `pathing` flag which enables pathing by default.
- Added NOPATHING flag to disable pathing entirely, useful for maps that have pathing enabled.
- Added `ReachedNode(Actor mo)` virtual, responsible for handling node traversal.
- Nodes now make use of MeleeRange to limit their sight checking functions.

src/scripting/thingdef_data.cpp

@@ -355,6 +355,7 @@ static FFlagDef ActorFlagDefs[]=
 	DEFINE_FLAG(MF9, DECOUPLEDANIMATIONS, AActor, flags9),
 	DEFINE_FLAG(MF9, PATHING, AActor, flags9),
 	DEFINE_FLAG(MF9, KEEPPATH, AActor, flags9),
+	DEFINE_FLAG(MF9, NOPATHING, AActor, flags9),
 
 	// Effect flags
 	DEFINE_FLAG(FX, VISIBILITYPULSE, AActor, effects),