We already support scoped WikiPageNames, but I guess
we could improve a bit the readability of those names.
If we're in a page belonging to a given "namespace", that leading prefix
could be omitted when displaying references to other pages sharing
the same namespace.
E.g. in the page TracDev/DatabaseSchema a reference to
TracDev/DatabaseUpgrades would read DatabaseUpgrades
(it would still have to be written in full, though).
This would be useful if we move all Trac documentation pages
in TracGuide/<something> or TracHelp/<something>, as it's
sometimes requested.
