Fixes to gcalendar.R

Hi John,
I've been using gWidgets2.  Thank you VERY much, it is easy to use and works well.
I've made some fixes for gcalendar under gWidgets2tcltk so that changes are seen by R.
Events such as Return, FocusOut and Button-1 were not causing any change in svalue for gcalendar.
Added handers for Return and FocusOut in the text widget, and invoke set_value() from the Button-1 binding for calendar day, so that invoke_change_handler() is called.
The problems were not seen in  gWidgets2GTK2.
Thanks again,
Gordon