mod_storage_s3: Enable connection pooling added in latest trunk Speed boost, something like a 30% improvement with http://localhost Small risk of failed requests due to limits on number of requests per connection or timeouts.

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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.