11462 indexer log (rebased onto develop)



This is the same as gh-1591 but rebased onto develop.

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Lower purge warning from ERROR to WARN. This can be tested by creating an object and then immediately deleting it. In `var/log/Indexer-0.log` there should be a WARN message of the form: "Null returned! Purging since cannot index ... ".

Open to suggestions to lower this further to INFO or DEBUG.

/cc @manics