[Patch] Uglify some names in _Rb_tree

[Paolo Carlini]

Howard Hinnant wrote:

> You got my attention. ;-)

Howard, while I finish preparing the patch proper +  some tests for
multimap (I hope to have something by tomorrow), can you suggest a
stategy for testing multiset (wrt the insert at lower bound thing)?!? At
the moment, I have big troubles, if I'm not allowed to look "inside" the
implementation details (something usually we don't do).

Thanks,
Paolo.