handle lack of ALIASING and SIMPLE_PRESENCE

[dsd]

OLPC OS 11.2.0 candidate 871:

See model/neighborhood.py class _Account

when connecting gabble to jabber.sugarlabs.org, the CONNECTION_INTERFACE_ALIASING and CONNECTION_INTERFACE_SIMPLE_PRESENCE interfaces are not available in self._connection. This causes get_self_handle_cb to raise an exception.

Various other interfaces are optional in this function; should these 2 be made optional as well? Or are they important enough that we should disconnect from the server and refuse to collaborate over it? Or should they always be available, reflecting a local telepathy-gabble problem?