Fixed stale database connection release
 - getAutoCommit, rollback and commit can throw exceptions
   on stale connections, which was preventing
   a correct connection release
narrowed catch clause in connection-release,
 changed loglevel to error
Merge pull request #1526 from rofreytag/db_realeasecon_fix

The methods getAutoCommit, rollback and commit can throw exceptions on stale connections. This PR implements corrected error handling during the connection releasing process so bad connections don't just hang around.