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
core: change ownership of debug log file before dropping privileges refs #3521

Opening the debug file, non-existing, will create it as root, before
actually dropping the privileges (644). When the core receives a SIGHUP
later, the non-privileged user cannot write to the debug file anymore,
bailing early.
In order to solve that, it's required to chown the debug log file to the
icinga user before dropping privileges.
possible fix for CVE-2012-6096 (nagios), added Icinga specific fixes

refs #3532
Merge branch 'mfriedrich/core' into next