Make "No" button default in the assert dialog

This makes more sense than the default default (sic) "Yes" button,
pressing which accidentally could kill the program if not running under
the debugger.

src/common/appbase.cpp

@@ -1307,7 +1307,7 @@ bool DoShowAssertDialog(const wxString& msg)
               wxT("further warnings.");
 
     switch ( ::MessageBox(NULL, msgDlg.t_str(), wxT("wxWidgets Debug Alert"),
-                          MB_YESNOCANCEL | MB_ICONSTOP ) )
+                          MB_YESNOCANCEL | MB_DEFBUTTON2 | MB_ICONSTOP ) )
     {
         case IDYES:
             // If we called wxTrap() directly from here, the programmer would