SI-8213 AnyRefMap.getOrElseUpdate is faulty

Altered getOrElseUpdate to be robust to the map changing out from under it as a result of calling the default value method.  Side-effects FTW!

Made a comparable change in LongMap also, as it was also affected.  And added a test to SetMapConsistencyTest.
Merge pull request #3434 from Ichoran/issue/8213

SI-8213 AnyRefMap.getOrElseUpdate is faulty