Allow multiple actions per frame

- You can now call several actions from one frame by grouping them between
  curly braces. i.e. :
   POSS G 3 { A_Pain; A_Log("Ow! That hurt!"); }
  I will probably add an `if (something) { blah; blah; } else { wah; wah; }`
  construct later, but that's the extent of the munging I plan for DECORATE. The
  real work goes to the scripting language, not here. But if this branch is
  getting merged to master sooner than later, here's an immediate benefit
  from it right now.

src/thingdef/thingdef_expression.cpp

@@ -3004,6 +3004,28 @@ ExpEmit FxActionSpecialCall::Emit(VMFunctionBuilder *build)
 	return dest;
 }
 
+//==========================================================================
+//
+//
+//
+//==========================================================================
+
+ExpEmit FxTailable::Emit(VMFunctionBuilder *build)
+{
+	return Emit(build, false);
+}
+
+//==========================================================================
+//
+//
+//
+//==========================================================================
+
+VMFunction *FxTailable::GetDirectFunction()
+{
+	return NULL;
+}
+
 //==========================================================================
 //
 // FxVMFunctionCall
@@ -3011,7 +3033,7 @@ ExpEmit FxActionSpecialCall::Emit(VMFunctionBuilder *build)
 //==========================================================================
 
 FxVMFunctionCall::FxVMFunctionCall(PFunction *func, FArgumentList *args, const FScriptPosition &pos)
-: FxExpression(pos)
+: FxTailable(pos)
 {
 	Function = func;
 	ArgList = args;
@@ -3082,15 +3104,10 @@ FxExpression *FxVMFunctionCall::Resolve(FCompileContext& ctx)
 //
 //==========================================================================
 
-ExpEmit FxVMFunctionCall::Emit(VMFunctionBuilder *build)
-{
-	return Emit(build, false);
-}
-
 ExpEmit FxVMFunctionCall::Emit(VMFunctionBuilder *build, bool tailcall)
 {
 	assert(build->Registers[REGT_POINTER].GetMostUsed() >= 3);
-	int count = ArgList->Size();
+	int count = GetArgCount();
 
 	// Emit code to pass implied parameters
 	if (Function->Flags & VARF_Method)
@@ -3105,9 +3122,12 @@ ExpEmit FxVMFunctionCall::Emit(VMFunctionBuilder *build, bool tailcall)
 		count += 2;
 	}
 	// Emit code to pass explicit parameters
-	for (unsigned i = 0; i < ArgList->Size(); ++i)
+	if (ArgList != NULL)
 	{
-		(*ArgList)[i]->Emit(build);
+		for (unsigned i = 0; i < ArgList->Size(); ++i)
+		{
+			(*ArgList)[i]->Emit(build);
+		}
 	}
 	// Get a constant register for this function
 	int funcaddr = build->GetConstantAddress(Function->Variants[0].Implementation, ATAG_OBJECT);
@@ -3132,6 +3152,24 @@ ExpEmit FxVMFunctionCall::Emit(VMFunctionBuilder *build, bool tailcall)
 	}
 }
 
+//==========================================================================
+//
+// FxVMFunctionCall :: GetDirectFunction
+//
+// If the function is not passed any explicit arguments, returns the
+// function. Otherwise returns NULL.
+//
+//==========================================================================
+
+VMFunction *FxVMFunctionCall::GetDirectFunction()
+{
+	if (GetArgCount() == 0)
+	{
+		return GetVMFunction();
+	}
+	return NULL;
+}
+
 //==========================================================================
 //
 //
@@ -3221,6 +3259,58 @@ ExpEmit FxGlobalFunctionCall::Emit(VMFunctionBuilder *build)
 	return v;
 }
 
+//==========================================================================
+//
+// FxSequence :: Resolve
+//
+//==========================================================================
+
+FxExpression *FxSequence::Resolve(FCompileContext &ctx)
+{
+	CHECKRESOLVED();
+	for (unsigned i = 0; i < Expressions.Size(); ++i)
+	{
+		if (NULL == (Expressions[i] = static_cast<FxTailable *>(Expressions[i]->Resolve(ctx))))
+		{
+			delete this;
+			return NULL;
+		}
+	}
+	return this;
+}
+
+//==========================================================================
+//
+// FxSequence :: Emit
+//
+//==========================================================================
+
+ExpEmit FxSequence::Emit(VMFunctionBuilder *build, bool tailcall)
+{
+	for (unsigned i = 0; i < Expressions.Size(); ++i)
+	{
+		ExpEmit v = Expressions[i]->Emit(build, tailcall ? i == Expressions.Size()-1 : false);
+		// Throw away any result. We don't care about it.
+		v.Free(build);
+	}
+	return ExpEmit();
+}
+
+//==========================================================================
+//
+// FxSequence :: GetDirectFunction
+//
+//==========================================================================
+
+VMFunction *FxSequence::GetDirectFunction()
+{
+	if (Expressions.Size() == 1)
+	{
+		return Expressions[0]->GetDirectFunction();
+	}
+	return NULL;
+}
+
 //==========================================================================
 //
 //==========================================================================