Changed to a left leaning red black tree implementation

Changed to a left leaning red black tree implementation

This change takes the algorithm as presented in Robert
Sedgewick's paper
[Left-leaning Red-Black Trees](http://www.cs.princeton.edu/~rs/talks/LLRB/LLRB.pdf)
and implements it in C#.  The implementation is a fairly
direct transliteration of the paper.

The code is integrated with the previous code's harness, but
little else remains.

If the DEBUG property is set, then it checks the invariants
of the tree are re-established after each insert and delete.

Commit migrated from https://github.com/dotnet/coreclr/commit/705b02f49968690b97558f34ad7bdb40b84ed36c