Fix an error on compilers without SFINAE.
Merged revisions 44470 via svnmerge from https://svn.boost.org/svn/boost/branches/unordered/trunk
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r44470 | danieljames | 2008-04-16 18:36:26 +0100 (Wed, 16 Apr 2008) | 2 lines
Missing semi-colon.