Holds the state of the deleted issue object more consistent before it gets deleted.
Makes parentId (and thus information, if the issue is a sub-task) accessible in thread local cache and
collects custom fields values (also making them accessible in thread-local cache).
See also:
http://jira.atlassian.com/browse/JRA-12091
http://jira.atlassian.com/browse/JRA-24331
http://jira.atlassian.com/browse/JRA-21646