Changes during Git migration:

- Added Extended Allocator support for Boost.Container.
- Improved Doxygen generated reference
- Fixed ticket #9338 ("VS2005 compiler errors in swap() definition after including container/memory_util.hpp")
- Modified relational operators to be friend inline definitions. This allows compilation checking when instantiating classes, avoids predeclarations and results in less verbose code.

- First to make associative containers' tree implementation configurable.
Refactored tree cloners into a single standalone class to avoid unnecessary instantiations and simplify maintenance.