Update IntervalTree

[PatrickNorton]

The version of IntervalTree we are using has received many upstream updates, however these have not been merged into here since 2013.

• I signed CLA
• I made sure the code in the PR follows the coding rules
• I made sure the code compiles on my machine
• I made sure there are no unnecessary changes in the code
• I made sure the title of the PR reflects the core meaning of the issue you are solving
• I made sure the commit message(s) contain a description and answer the question "Why do those changes fix that particular issue?" or "Why are those changes really necessary as improvements?"
• I made sure the commit message title starts with "fix #424242:" if there is a related issue
• I created the test (mtest, vtest, script test) to verify the changes I made

[Jojo-Schmitz]

The logs for the failing utests are wiped meanwhile, so no idea what they are failing on. Maybe a rebase is in order?

[vpereverzev]

@PatrickNorton could you rebase your branch onto the latest master? I'm not against of merging this. But we need to make sure that unit-tests are not failing

[Jojo-Schmitz]

As @PatrickNorton seems to have been inactive for quite a while, I git cherry-pickd the stuff on top of the current master, see #11279

[cbjeukendrup]

Closing as replaced by #11279