- hold a lock while accessing the tree of delayed values
- use weak reference counts with the owner object to avoid doing
g_object_notify on a dead object
- dispatch the "has-unapplied" notify to the proper main context
This commit fixes up a few race conditions in the GSettingsBackend, mostly with
respect to change notifications occuring at the same time as the last reference
count on a GSettings is dropped. With GDBus feeding us our incoming signals in
a separate thread, this is something that could easily happen.
