mod_storage_xmlarchive: Fix "user" iteration API Fixes use in prosody-migrator. Otherwise this particular API is not used much, or this would have been noticed before. Usually it is a different store like 'accounts' that is responsible for providing the authoritative list of users. Thanks Ge0rG for testing

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summary: Extra verbose logging of sent and received
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Summary
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Sometimes it is useful to get the raw XML logs from clients for
debugging purposes, but some clients don't expose this.

This module logs dumps everything sent and received into debug logs, for
debugging purposes.