Python scripts could perform actions that created notifiers
which would not be handled until the script was complete.
In the case of adding & removing objects a notifier would be created
for adding the object, then cleared when the ID was removed.
This lead to the notifier queue filling up with cleared notifiers
which were included in the search whenever an ID was removed.
The result of this was that adding and removing objects from a script
would become increasingly slower & use more memory.
Resolve by storing the current notifier being handed which isn't freed
(only cleared). The notifier handling loop detects cleared notifiers
and frees them after use.
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