- A Template is explicitly disallowed

  from having a url that normalizes to relative outside
  of the root.   That is, if the Lookup is based
  at /home/mytemplates, an include that would place
  the ultimate template at
  /home/mytemplates/../some_other_directory,
  i.e. outside of /home/mytemplates,
  is disallowed.   This usage was never intended
  despite the lack of an explicit check.
  The main issue this causes
  is that module files can be written outside
  of the module root (or raise an error, if file perms aren't
  set up), and can also lead to the same template being
  cached in the lookup under multiple, relative roots.
  TemplateLookup instead has always supported multiple
  file roots for this purpose.
  [ticket:174]