GCancellable hints

[Richard Hughes <hughsient gmail com>]

In the last few weeks I subclassed GCancellable into a ZifCancellable
object, which allowed me to complete a personal project. I now want to
do the same for PackageKit, and think perhaps the functionality should
be abstracted and pushed upstream into Glib as it's the second time
I'm doing this. I'm asking for your opinions to see if it's the sort
of thing you want in Glib.

For me, a "task" can often do actions that cannot be cancelled for
some time (when dealing with hardware and calling out to other
programs), so for PackageKit, the install method:

* depsolves (user can cancel)
* downloads a package (user can cancel)
* installs the package using rpm/apt/etc (user CANNOT cancel)
* updates databases (user can cancel)

And in the UI, we want to make the [Cancel] button insensitive for
some of the actions rather that letting the user click it and wait for
ages with no feedback.

The only functionality that ZifCancellable adds is two methods:

void zif_cancellable_set_hint (GCancellable *cancellable, gboolean can_cancel);
gboolean zif_cancellable_get_hint (GCancellable *cancellable);

And added the "hint-changed" signal

void hint_changed_cb (GCancellable *cancellable, gboolean can_cancel,
gpointer user_data)

Better names welcome. Anyway, I would appreciate your opinions on this
and if it would be accepted upstream.

Thanks,

Richard.