Priorities of model listeners added via the IoC testing framework have become inverted

The bug fixes for applying precise model invalidation and the new "source tracking system" merged in https://github.com/fluid-project/infusion/pull/553 for FLUID-5489, FLUID-5490 introduced a serious bug into the system whereby the "mapPriority" function is applied twice to model listener records added via the IoC testing framework. For example, in the following record,
listenerMaker: "gpii.tests.makeAssertModelChanges",
makerArgs: ["

{resourceInputPanel}", "resources.0.src", "{that}.options.testOpts.0.src"],
spec: {path: "", priority: "last"},
changeEvent: "{resourceInputPanel}

.applier.modelChanged"
the value priority: "last" became mapped to a numeric value, and was then inverted, causing this listener to be notified FIRST rather than last. This causes the test cases to fail in a brutal and perplexing way - firstly the entire test sequence resolves before the second change in the stack (triggered by a manual relay) is applied, and so no changes are picked up in the UI - then when the changes do begin to apply, the user receives an "error expanding material for destroyed component" failure since the entire test fixture has now been cleared away.