Crosshatch in XPointer, XLink (was Last call comments on XML Bas e)

Martin wrote:

> There is a very minor I18N comment to change 'crosshatch'
> to 'number sign' (the official name of #).

Per the WG resolution to accept this comment, I have changed this in XML
Base.  I stole the wording directly from XLink and XPointer, so I assume
they should to be changed before PR as well.

- Jonathan Marsh