* Added a new type of Exception
for better recognition of connection failures
* Added more logging for mysql communication
* Retries on connection loss during query.
Make MySQL dictionary source resilient to unexpected loss of connection
during querying MySQL. This behavior is controlled with
".fail_on_connection_loss" config parameter, which defaults to false.
* Stripped some debugging leftover garbage
* Minor followup corrections
* Corrections after PR comments
* Yet more fixes
