- made arbitrary portals passable.

This includes:

* allow one sided portal linedefs to be crossable when part of a polyobject. Due to the limitations, two-sided linedefs won't work here. For general use this is still not allowed because making them passable would require some crippling fudging.
* delay portal finalization until after polyobjects have been spawned.
* the camera interpolation also needs to handle angle differences.

The code is still not 100% complete - the most important thing that is still missing is proper handling of P_CheckPosition through arbitrary portals.

src/p_setup.cpp

@@ -4045,7 +4045,8 @@ void P_SetupLevel (const char *lumpname, int position)
 
 	times[16].Clock();
 	if (reloop) P_LoopSidedefs (false);
-	PO_Init ();	// Initialize the polyobjs
+	PO_Init ();				// Initialize the polyobjs
+	P_FinalizePortals();	// finalize line portals after polyobjects have been initialized. This info is needed for properly flagging them.
 	times[16].Unclock();
 
 	assert(sidetemp != NULL);