boostorg/multi_array — pull request #6 by MarcelRaad (2014-09-26 08:54:36+00:00)
Title: Fix clang warning

clang complains about the friend declaration with a warning:

warning : unqualified friend declaration referring to type outside of the nearest enclosing namespace is a Microsoft extension; add a nested name specifier [-Wmicrosoft]
friend class iterator_core_access;
^
::boost::

Explicitly qualifying the class name with its namespace fixes the warning.