GTK+ menu stock item support

[Robert Roebling]

 Hi,

currently wxID_ABOUT causes

 Gtk-CRITICAL **: file gtkstock.c: line 128 (gtk_stock_lookup):
assertion `stock_id != NULL' failed

when uses with my GTK+ 2.2.3. I haven't been able to 
spot the cause quickly. Could the author of the patch
look into that?

  Robert