DefaultIndexManager.hold/release can be used to temporarily postpone issue reindexing.

GreenHopper uses this feature in the epic link creation logic, as each issue otherwise gets reindexed several times which turned out to be a big
performance issue.

Problem: In case the same issue is indexed multiple times, DIM keeps the oldest instead of the newest issue around.

I debugged the problem with tcampbell and it should be a trivial fix only.