This adds more tests to ensure we're not following symlinks through a
directory.

This ensures that we also handle some other variants like when the model
is set or when we have signal ordering that could perhaps keep us from
having widgets created by models yet.

Fixes: GNOME/libdazzle#21

This allows async loading of icons where the caller only needs to
g_object_notify() for "icon" to ensure that the view updates the image.

Jan-Michael Brummer authored Jul 29, 2018 and Christian Hergert committed Jul 30, 2018

Clears text before signaling prevents accidential text removal.

Fixes: GNOME/libdazzle#17

This helps us ensure that the tree is destroyed during cleanup which makes
tracking leaks easier.

We don't need to use dzl_clear_pointer() anymore now that GLib has access
to g_clear_pointer() that performs similar checks as dzl_clear_pointer().

We need to ensure that the grab does not disappear out from under us. We
also want to make sure that we have ownership of the widgets during the
processing of the events.

This adds a new reference to self during the operation, and references all
the potential widgets before doing notifications.

This variant is not floating, and therefore we need to release it.

g_variant_parse() does not return a variant with a floating reference. So
we must unref them ourselves. Aldo, don't try to ref_sink(), since that
just increments to 2, and is not what we want.

If we are find data to release during our final unref, we should free
it using our destroy callback.

This fixes test-ring under ASAN.

We don't really need to maintain any of the pointers here after dispose,
so just drop data as soon as we can.

We are responsible for clearing this, so make sure we do so.

This adds a simple magic value we can use to assert the struct type. A
little bit useful while tracking down some missuse bugs.

Make sure that we release the return value if there is any for the
call. In most cases there isn't.