print a message if db unlocking fails in sx_hashfs_check
print a message if db unlocking fails in sx_hashfs_extract
try to not send negative counters

we can have multiple counters for same (block,replica) with different
rebalance ages (for example: file uploaded then rebalanced then deleted later,
                etc.)
When rebalancing/repairing send the sum of the counters for a given
(block,replica) which should be >= 0 outside of rebalance.
Still if a counter is negative don't overflow it to unsigned.
be consistent about counter size: its not 64-bit