org-export: Change output from org-export-resolve-fuzzy-link

org-export: Change output from org-export-resolve-fuzzy-link

* contrib/lisp/org-export.el (org-export-resolve-fuzzy-link): Now
  return the full object (for a target) or element (for an headline)
  when a match is found.  Also rewrite internals so it doesn't rely
  on :headline-alist.
(org-export-collect-tree-properties): Remove :headline-alist property
  from communication channel, since `org-export-resolve-fuzzy-link'
  doesn't use it anymore. Also store full target objects
  in :target-list property, not only raw names. Fix an argument name
  mismatch, too.

Previous version of org-export-resolve-fuzzy-link returned beginning
position as the identifier for the headline found, which is pretty
weak when files are included in the parsed buffer.