libatspi currently listens for ChildrenChanged, PropertyChange, and
StateChanged events but does not call RegisterEvent for them.
Intending to come up with a better fix for 2.2.

When we receive strings from atk, we should ensure that they are valid UTF-8
before sending them over D-Bus, since bad UTF-8 will cause dbus-daemon to
kill the connection.

currentValue for obvjects implementing the AtkValue interface.

Bug #35524

If a new version of libdbus is available, use DBUS_ERROR_UNKNOWN_OBJECT,
DBUS_ERROR_UNKNOWN_PROPERTY, and DBUS_ERROR_PROPERTY_READ_ONLY when
appropriate.

Remove function to get the accessibility bus, since it was duplicating code
in at-spi2-core and should be modified for BGO#644851.
Also, use atspi_dbus_*_setup_with_g_main instead of depending on dbus-glib,
so that FDO#35115 doesn't show up and we don't need to disable p2p if an old
version of dbus-glib is installed.

Note that at-spi2-atk now depends on libatspi where previously it did not.