move set_timezone function to record.inc.php (that's the only place where it's
being used at the moment) in preparation for an update to dynamic_update.php
which will require set_timezone to be in an accessible place (where an active
session is not available)
call update_soa_serial after dynamic update of record. This will notify
PowerDNS of the changes, which will in turn trigger a notification to (followed
by AXFR from) slave nameservers
Merge pull request #208 from sjvs/bugfixes/update-soa-after-dynamic-update

Update SOA record after dynamic update (fixes #181)