Note that OBJECT_HAS_TOGGLE_REF() is no longer used. This is good and
bad.
What we soon will do, is drop the OPTIONAL_BIT_LOCK_TOGGLE_REFS lock,
and only call g_datalist_id_update_atomic(). This way, we only need to
take the GData lock.
However, g_datalist_id_update_atomic() also needs to do a linear search
for quark_toggle_refs key. Previously, with OBJECT_HAS_TOGGLE_REF() we
didn't require this.
So the new approach is only faster, if searching the GQuark key is
reasonably fast. GData makes an effort to implement fast lookup, so
this is suppoed to be fine.
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