Description:
------------
Unable to get GtkEntry to have focus after user selects a row in GtkTreeView on same screen w/o a grab_default.  Widget->grab_default causes GtkCritical error w/o can_default (php.exe:2020 Gtk-CRITICAL gtk_widget_grab_default: assertion 'GTK_WIDGET_CAN_DEFAULT'(widget) failed.  Widget->can_default causes PHP fatal error and crash.

Reproduce code:
---------------
<?php 
$button1 = new GtkButton('Default Test');
$button2 = new GtkButton('Extra Button');
$button2->can_default(TRUE);

$vbox = new GtkVBox;
$vbox->pack_start($button1, FALSE, FALSE);
$vbox->pack_start($button2, FALSE, FALSE);
 
$window = new GtkWindow;
$window->connect_simple('destroy', array('gtk', 'main_quit'));
$window->set_default_size(120,120);
$window->add($vbox);
$window->show_all();

$button2->grab_focus();
$button2->grab_default();

Gtk::main();

 ?> 


Expected result:
----------------
Button has keyboard focus and no critical error for can_default property.

Actual result:
--------------
application crash.