- stop using the ATAGs for checking pointer types in asserts.

This is an incredibly costly way to do a debug check as it infests the entire VM design from top to bottom. These tags are basically useless for anything else but validating object pointers being passed to native functions (i.e. mismatches between definition and declaration) and that simply does not justify a feature that costs execution time in non-debug builds and added memory overhead everywhere.
Note that this commit does not remove the tags, it only discontinues their use.

src/scripting/vm/vmexec.cpp

@@ -82,7 +82,6 @@ void ThrowVMException(VMException *x);
 #define ASSERTF(x)		assert((unsigned)(x) < f->NumRegF)
 #define ASSERTA(x)		assert((unsigned)(x) < f->NumRegA)
 #define ASSERTS(x)		assert((unsigned)(x) < f->NumRegS)
-#define ASSERTO(x)		assert((unsigned)(x) < f->NumRegA && reg.atag[x] == ATAG_OBJECT)
 
 #define ASSERTKD(x)		assert(sfunc != NULL && (unsigned)(x) < sfunc->NumKonstD)
 #define ASSERTKF(x)		assert(sfunc != NULL && (unsigned)(x) < sfunc->NumKonstF)
@@ -235,3 +234,23 @@ void VMFillParams(VMValue *params, VMFrame *callee, int numparam)
 }
 
 
+#ifdef _DEBUG
+bool AssertObject(void * ob)
+{
+	auto obj = (DObject*)ob;
+	if (obj == nullptr) return true;
+#ifdef _MSC_VER
+	__try
+	{
+		return obj->MagicID == DObject::MAGIC_ID;
+	}
+	__except (1)
+	{
+		return false;
+	}
+#else
+	// No SEH on non-Microsoft compilers. :(
+	return obj->MagicID == DObject::MAGIC_ID;
+#endif
+}
+#endif