object on the panel to take account of the fix to bug 50339 which
requires that a widget in a GtkWindow have focus initially, rather
than the GtkWindow itself.

* basep-widget.[ch]: Rename focus_return as the more meaningful name
focus_panel. Remove the functions basep_widget_focus_in_event,
basep_widget_focus_out_event and basep_widget_set_focus. Specify
focus chain in basep_widget_construct so that focus goes initially to
the panel.

* panel-widget.[ch]:
Add functions panel_widget_focus_in_event, which sets PRELIGHT state
for panel and adds keybindings for Tab and Shift+Tab, and
panel_widget_focus_out_event, which unsets the PRELIGHT state for the
panel, removes keybindings for Tab and Shift+Tab and unsets
GTK_WIDGET_CAN_FOCUS flag, if focus is going to another widget in the
window. Rename move_to_panel to tab_move.
Add key bindings for Tab and Shift+Tab when panel has focus or when in
move mode. Set GTK_WIDGET_CAN_FOCUS flag on panel when it is created.
Add code to panel_widget_tab_move to move focus to object in panel;
this requries unsetting GTK_WIDGET_CAN_FOCUS flag on panel.
Add function panel_widget_focus which moves the focus from an object
on the panel to the panel.