getAddressString is deprecated, use addressString

The documentation says addressString is available with OS X 10.2 and
newer.
Use deviceWithAddress instead of withAddress

I'm unsure when this was deprecated.  The documentation says that it is
available with OS X 10.7 and newer.
Update rbt_device_rssi and rbt_device_link_quality

In OS X 10.7 and newer the old way of retrieving the RSSI and link
quality are no longer supported.  It appears that the extension's RSSI
method maps to [IOBluetoothDevice rawRSSI] and the link_quality method
to [IOBluetoothDevice RSSI].

The bluetooth extension no longer works on OS X 10.6 and earlier because
I don't know how to detect OS X methods in the framework.  When someone
complains the old behavior can be restored.