Detectin mainloop integration

[Havoc Pennington]

Hi,

This looks pretty good to commit, to me, if nobody else has objections. 
Ideally commit to dbus-glib at the same time so we can start getting 
some testing.

Two very small changes:

  - DBUS_DEPRECATED should be considered internal/private API to 
libdbus, so not used in dbus-glib. Renaming to _DBUS_DEPRECATED would 
not be bad, but should be in a separate patch from this patch.

  - if you make dbus-glib configure require dbus-1 >= 1.1.3, it might be 
an easier error message for people to figure out (right now the error 
will be "no dbus-glib-main" which doesn't clarify where to get that)

Regarding leaking the integration from dbus_g_bus_get(), I think it will 
not matter at all in practice.

Havoc