Trying to add an exit confirmation dialog to Cygwin setup.exe, failing

[Terry Fleming]

$ diff original/setup-2.573.2.3/propsheet.cc setup-2.573.2.3/propsheet.cc
164a165,169
> if(((uMsg==WM_SYSCOMMAND)&&((wParam&0xfff0)==SC_CLOSE))||
> 	(((uMsg==WM_COMMAND)&&(wParam==2))))
> 		if(MessageBox(hwnd,
> 			"Are you sure you want to exit setup? Any current download or installation will be aborted.",
> 			"Exit Cygwin Setup?", MB_YESNO)==IDNO) return 0;

Original:
http://cygwin.com/setup/current/setup-2.573.2.3.tar.bz2