[Issue 12915] RedBlackTree leaks memory

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12915

--- Comment #1 from Steven Schveighoffer <schveiguy at yahoo.com> ---
Can we just null the end node's pointers on the destructor? this should
dereference all the nodes.

BTW, I think there is a previous bug on that same behavior:
https://issues.dlang.org/show_bug.cgi?id=5650

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