The MPL version is slower to compile and `BOOST_STATIC_ASSERT` is
already used in some places. So unify that.
This also fixes `Wzero-as-null-pointer-constant` warnings, see https://github.com/boostorg/mpl/pull/75
is_incrementable.hpp: checks whether ++x is well-formed
pointee.hpp: value_type of iterators or smart pointers
indirect_reference.hpp: reference type of iterators or smart pointers
indirect_iterator.hpp
indirect_iterator_member_types.cpp
Use pointee/indirect_reference to select value/reference type.
iterator_concepts.hpp: Fixed interoperable test. Hardly tests enough, but it's a start
minimum_category.hpp: Better error messages for vc6
indirect_iterator_test.cpp: Workarounds for compilers without SFINAE
static_assert_same.hpp: Informative error reports; added a macro.
zip_iterator_test.hpp: Added missing #include
Jamfile: made zip_iterator test pass with vc6/stlport
[SVN r21514]
