Change "are you sure you want to close this window" default back to what it

was ("yes"). Partly because it was inconsistent with gtkdlg.c, and partly
because it was annoying me.

[originally from svn r5371]

windows/window.c

@@ -1860,7 +1860,7 @@ static LRESULT CALLBACK WndProc(HWND hwnd, UINT message,
 	    if (!cfg.warn_on_close || session_closed ||
 		MessageBox(hwnd,
 			   "Are you sure you want to close this session?",
-			   str, MB_ICONWARNING | MB_OKCANCEL | MB_DEFBUTTON2)
+			   str, MB_ICONWARNING | MB_OKCANCEL | MB_DEFBUTTON1)
 		== IDOK)
 		DestroyWindow(hwnd);
 	    sfree(str);