Generalize overflowLeaf to also handle overflows in branch nodes.
Generalize overflowLeaf to also handle overflows in branch nodes.

This doesn't quite work yet because the calls to treeDecrement and treeIncrement
operate at the leaf level, not on pathNode(Level) as required.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@120068 91177308-0d34-0410-b5e6-96231b3b80d8

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