Dynamic field updates should pass OldValue to Event and History

Dear all,

currently the value prior to an update of a dynamic field can only be recalculated from history which is fairly expensive.

Supplying the "OldValue" as part of the TicketDynamicFieldUpdate_* event allows an event handler to react on certain _changes_ in value (e.g. increase, decrese) without digging into the history.
Recovery from history again is eased by adding the OldValue as an extra item in the "Name" field.
--
Somehow my GitHup repo is out of sync with the orginal otrs repo; the commit I refer to is the one from January 27 (1 ahead of upstream/rel-3_3).

best regards,
 Dietmar