Use of Gtk3::Gdk::EventMask with Gtk3::Widget::{set,get,add}_events

[Zakariyya Mughal <zaki mughal gmail com>]

Hello,

I noticed that the methods

    $widget->set_events( ... )
    $widget->get_events( ... )
    $widget->add_events( ... )

did not seem to be taking a `Glib::Flags` of type `Gtk3::Gdk::EventMask`
as would be expected by reading the documentation. Looking at the
`gtk+-3` source code, I see that the function signatures are using
`gint` instead of `GdkEventMask`. It looks like the type annotation
needs to be updated.

While I could try to use `Glib::Type->list_values` or `${ Gtk3::Gdk::EventMask->new(...) }`,
this behaviour is surprising.

I found similar bugs in the Bugzilla here:

- Bug 642238 - [introspection] Type information not available in generated GIR files 
  <https://bugzilla.gnome.org/show_bug.cgi?id=642238>,

- Bug 711873 - [introspection] no way to gtk_widget_set_events()
  <https://bugzilla.gnome.org/show_bug.cgi?id=711873>.


Regards,
- Zakariyya Mughal