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

NEWS.mdtext

@@ -1,8 +1,14 @@
 # InDefero 1.2 - xxx xxx xx xx:xx 2011 UTC
 
+ATTENTION: You need Pluf [324ae60b](http://projects.ceondo.com/p/pluf/source/commit/324ae60b)
+or newer to properly run this version of Indefero!
+
 ## New Features
 
-## Bugfixes 
+- Indefero's issue tracker can now bi-directionally link issues with variable, configurable
+  terms, such as "is related to", "is blocked by" or "is duplicated by" (issue 638)
+
+## Bugfixes
 
 - monotone zip archive entries now all carry the revision date as mtime (issue 645)
 - Timeline only displays filter options for items a user has actually access to (issue 655)