Heya,

Some time ago I had problems with client.c's architecture. It would
allow me to easily report completed discoveries without causing crashes.

The attached patch moves all the static variables into the main
BluetoothClient object, and instead of return a new object when using
_new() we return an existing instance of the client.

This makes no changes to the external API for the BluetoothClient, and
should work just as well as older versions did.

A couple of bugs I found in client.c:
- launch test-client with a dongle inserted, remove and reinsert the
dongle, the bdaddr of the device is not set anymore
- launch test-client without a dongle inserted, insert it, the bdaddr is
not set and there's no children to the adapter (although there are if
inserted when started)
- launch test-client with a dongle inserted, remove it, add another one,
the set of known devices underneath hasn't changed

All those problems exist in the old version of client.c, and I intend on
fixing them, as well as making the search button work as expected in the
device selection widget.

Cheers