Fix name clash problems with intrusive iterators.

When I recently tried to use the pretty printers for boost::intrusive::set/boost::intrusive::list in a new environment they just didn't work. Turned out the problem is a name clash. The names BoostIntrusiveListIterator and BoostIntrusiveSetIterator were used for both pretty printers and internal helpers. I don't know why things used to work anyway, but it doesn't matter. This commit fixes the problem

I also took the opportunity to clean up some formatting issues local to boost::intrusive::set/boost::intrusive::list (mainly got rid of the camel case).