Improve compiler compatibility (#743)

* fix returns

* use standard C headers

* struct/class mismatch

* explicit this in template

* switch variable scope

* C standard compliance

* & l-value

src/d/d_msg.cpp

@@ -7,7 +7,7 @@
 #include "dolphin/types.h"
 
 class J2DTextBox;
-class fopMsgM_pane_class;
+struct fopMsgM_pane_class;
 
 J2DPicture* button_icon[8];
 J2DPicture* button_kage[8];