Menugen: clashes in page-IDs

[Ichthyostega]

symptom

when using menus entry reordering directives in the Asciidoc source, an entry pointing to the mismatched sibling page with the same ID shows up in the menu

cause

the logic for assigning page IDs is overly simplistic. It is likely that pages with exactly the same ID, as derived from the name, show up in several sibling hierarchies

Example encountered in the research section. We have now two Froscon talks, with companying code examples, and both want to add a "Resources" sub page