Merge from TRUNK. Fix for Sourceforge bug #1450260 where this will assert on MSVC with /MDd:

    boost::format("%s") % std::string()


[SVN r33444]

libs/format

@@ -1 +1 @@
-Subproject commit e74675f9d061902af862ac7c2e5cc314f147c460
+Subproject commit d5240e728d2441f2d7ea7dc759a9351479de94aa