- fixed GCC warnings and errors

(Is there anyway to tone down GCC's warning level? It outputs too many false positives for potentially uninitialized variables in which the genuine errors get drowned.)

src/p_things.cpp

@@ -52,6 +52,7 @@
 #include "math/cmath.h"
 #include "actorptrselect.h"
 #include "g_levellocals.h"
+#include "actorinlines.h"
 
 // Set of spawnable things for the Thing_Spawn and Thing_Projectile specials.
 FClassMap SpawnableThings;