Pushing fixes over from the trunk to the release branch.
Fixes #5664
Fixes #4874

svn path=/branches/release/boost/multi_array/; revision=78496
Specialize BOOST_CHECK_MESSAGE handler now that array.cpp uses it.

svn path=/branches/release/libs/multi_array/; revision=78498
Pulling a patch from the trunk to release.  include enable_if.hpp where
needed.

svn path=/branches/release/boost/multi_array/; revision=78532