rename GetClassName/IsClass, declare mxtypes

Was intended as a simple code improvement, however it also seems to make WinMain, MxString::operator=, MxDSFile::Open 100% (all of which just needed registers to be switched around)

ISLE/isle.cpp

@@ -101,7 +101,7 @@ void IsleApp::Close()
     } while (lVar8 == 0);
 
     while (Lego()) {
-      if (Lego()->vtable28(ds) != MX_FALSE) {
+      if (Lego()->vtable28(ds) != FALSE) {
         break;
       }