- scriptified the functions in a_possessed.cpp and added the needed exports and constants.

- fixed: Script functions did not receive the function name when being created.
- relaxed the asserts for PARAM_STATE, because the VM knows nothing about ATAG_STATE. Any state variable's content (e.g. Actor.SeeState) will receive ATAG_GENERIC, rather than ATAG_STATE.
- added a 'NeedResult' flag so that certain operations can create shorter code if the result of the expression is not needed. So far only used for postdecrement/increment statements on local variables (which is the most frequent case where this matters.)
- fixed postincrement and decrement for local variables. Due to the result preservation semantics it created faulty code.

src/p_mobj.cpp

@@ -510,6 +510,14 @@ bool AActor::SetState (FState *newstate, bool nofunction)
 	return true;
 }
 
+DEFINE_ACTION_FUNCTION(AActor, SetState)
+{
+	PARAM_SELF_PROLOGUE(AActor);
+	PARAM_STATE(state);
+	PARAM_BOOL_OPT(nofunction) { nofunction = false; }
+	ACTION_RETURN_BOOL(self->SetState(state, nofunction));
+};
+
 //============================================================================
 //
 // AActor :: AddInventory