Corrected the group_changed signal vfunc declaration, adding the first

Corrected the group_changed signal vfunc declaration, adding the first

2004-03-03  Murray Cumming  <murrayc@murrayc.com>

        * gtk/gtkradiobutton.h, radiomenuitem.h: Corrected the group_changed
        signal vfunc declaration, adding the first parameter, which is the
        widget emitting the signal.