Optimize rebalance method by using null optimized list implementation.

rebalance method relies heavily on s.c.i.List. By replacing List with null
optimized version, NList, rebalance operation is significantly more faster.
Test indicate +10 % performance improvement for tree sizes >= 100.

Existing tests verify red-black tree invariants, including operations
involving tree rebalance.
Merge pull request #2219 from chuvoks/rbtRebalance

Optimize RedBlackTree rebalance method by using null optimized list implementation.