DESCRIPTION
    EscalatePriorityLinear is a ScripAction which is NOT intended to be
    called per transaction. It's intended to be called by an RT escalation
    daemon. (The daemon is called escalator).

    EsclatePriorityLinear uses the following formula to change a ticket's
    priority:

        Priority = InitialPriority + 
            (FinalPriority-InitialPriority) * (Now-Starts) / (DueDate-Starts)

    Unless the duedate is past, in which case priority gets bumped straight
    to final priority.

    Unlike RT::Action::EscalatePriority, priority is not decreased if it's
    above FinalPriority.