Use transactions for SQL queries (just for MySQL for now).

This experimental patch significantly increases IDO2DB's performance.
More testing is required to determine whether transactions are safe
for general use.
Added config option for SQL transactions
Added debug output for IDO transactions
correct config description for transactions, add as new config item to update location refs #3527
update Changelog for refs #3527
import 1.8.3 Changelog into dev tree
deprecate enable_sla refs #3450