Scribe links are often not redirected correctly if belonging to medium's
'global-identity' redirections. This is a first attempt at fixing those
by removing the superfluous string from the scribe URL.
Generalized enough to work as a 'post-processing' function for the
redirection plugin, which can be set up by pointing the 'postprocess'
key of a page entry to a callable object (most likely a function).
