[Evolution] Wombat termination

[Federico Mena Quintero <federico helixcode com>]

In the old, standalone Tlacuache PCS the whole PCS process terminated
when the singleton calendar factory lost its last reference count.
This was the only factory that the Tlacuache server managed, so that
was fine.

However, these days Wombat never terminates.  It may be launched when
any client requests that the PAS or PCS be activated; it actually
activates both of them and keeps running forever.

However, if all clients unref all their calendars, the factory will of
course be destroyed and Wombat will be left with only a running PAS,
which is wrong.

I am going to add a signal to the PAS and the PCS factory objects to
indicate that there are no more clients connected to them.  When
Wombat sees that none of the servers has any more clients, it will
terminate.

[If none of this makes sense, it's because it is 5:30 in the morning...]

  Federico