Finalize ticket relations (closes issue 638)

- IssueUpdate.php: use dynamically set field validators for dynamically
  created fields; let relation_type0 and relation_issue0 exist at any time;
  check the validity of a user selection and combine the various input fields
  if possible; do the database updates for links; change the "change" format
  for labels to a more precise structure and no longer trust on a leading
  dash for removed labels
- IssueCreate.php: change the validator calls and field names
- Issue.php (getGroupedRelatedIssues): make it possible to return only a
  flat list of integers for easier processing
- 17AddIssueRelations.php: migrate the previous serialized "changes" format
  for issue comments to the new, more structured format (up and down)
- js-autocomplete.html: add support for multiple input fields
- view.html: output relation changes and wrap the related issues stanzas into
  paragraphs
- NEWS.mdtext: note the addition and the need for a specific version of Pluf

src/IDF/Views/Issue.php

@@ -404,7 +404,7 @@ class IDF_Views_Issue
         $issue = Pluf_Shortcuts_GetObjectOr404('IDF_Issue', $match[2]);
         $prj->inOr404($issue);
         $comments = $issue->get_comments_list(array('order' => 'id ASC'));
-        $related_issues = $issue->getGroupedRelatedIssues(array('order' => 'creation_dtime DESC'));
+        $related_issues = $issue->getGroupedRelatedIssues(array('order' => 'other_issue ASC'));
 
         $url = Pluf_HTTP_URL_urlForView('IDF_Views_Issue::view',
                                         array($prj->shortname, $issue->id));