Improve retrieval of JIRA issues

[copernico]

While the retrieval of JSON is forbidden by most (all?) Apache projects, the XML format seems available. Example: https://issues.apache.org/jira/si/jira.issueviews:issue-xml/ZOOKEEPER-4557/ZOOKEEPER-4557.xml

Interesting: one can restrict the fields contained in the XML response, by appending field=key&field=summary&field=.....

Maybe this may make it simpler to also reason about "related" (e.g. duplicate) issues.