Allow 'any_cast' to a reference type.

The original patch from Mikhail Glushenkov.
Tests from Alexander Nasonov.

See:
   http://lists.boost.org/MailArchives/boost/msg76737.php
   http://lists.boost.org/MailArchives/boost/msg79043.php


[SVN r27416]

libs/any

@@ -1 +1 @@
-Subproject commit d76c077f317da9c9136d94ff1228268f298ca403
+Subproject commit 7a5eeffb81f85823a1aa76bbba0d00e6a7df3635