User can crash JIRA if SummaryIssueStatsCollector load too many issues

{{I've found that GH can load unbounded amounts of issues inside the class com.pyxis.greenhopper.jira.util.collector.SummaryIssueStatsCollector.

In this particular scenario, it has loaded 17637 Lucene documents, using up 85MB of heap.

Most likely the operation time out for the user, which blindly re-run the same operation 8 times before crashing JIRA, just this operation was using approximately 650MB of the available heap.}}