[gnome-db] event notifications

[Rodrigo Moya <rodrigo gnome-db org>]

Hi

I've just completed the addition of the event notification stuff, so
that we can now make the providers notify clients of anything we want to
(table created/dropped, transaction started, etc).

What I've done is:

* added "event_notification" signal to GdaClient
* added basic set ofevents (CONNECTION_OPENED, CONNECTION_CLOSED, ERROR)
* removed "error" signal on GdaClient
* added gda_client_notify_event function
* adapted mergeant to work with this new error notification

So, now we just have to define the set of events (and their parameters)
and start adding them to the providers, so that they can, via
gda_client_notify_event, notify of any change in the database.

So, comments?

cheers