function beginDocumentNavigation() {
        _documentNavPending = true;
    }
Indicate that changes to currentDocument are temporary for now, and should not update the MRU
ordering of the working set. Useful for next/previous keyboard navigation (until Ctrl is released)
or for incremental-search style document preview like Quick Open will eventually have.
Can be called any number of times, and ended by a single finalizeDocumentNavigation() call.