Updating a site menu item and swapping it from an external url to
a site file or vice versa was failing to create the correct type of
link on account of incorrect parameters. Unfortunately this can't
fix existing muddled links, as it has no way of knowing whether the
url value or the file value in the database is the one to use.

Change-Id: Ib8ac2da42125b020a1214b268c079f93166d2da8
Signed-off-by: Melissa Draper <melissa@catalyst.net.nz>