Need to disable keyboard accelerators Shift-Home and Shift-End when focus is in a dialog

[Lewis Rosenthal]

When clicking in the page number dialog in the toolbar for a lengthy document, it is expected to be able to highlight the entire page number (e.g., 1200) with Shift-Home. Unfortunately, we grab that key combination and jump to the first supported document in the directory, leaving the current document.

We should disable these accelerators when in that box, so that we do not lose the current document.