mod_storage_xmlarchive: Fix return of numeric 'when' from key-value API At some point, 'when' was stored as a timestamp string then as a numeric UNIX timestamp, so both cases needs to be handled, as they are elsewhere. Thanks spec/core_storagemanager_spec.lua

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summary: Log a message once per minute
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This module sends `-- MARK --` to the log once per minute. This may be
useful to give a sense of how busy the server is or see that logging and
timers are still working.