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 (n.b., I do not believe this accelerator or Shift-End has/have been documented, as yet), leaving the current document.

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