Mark <regex> unusable for all libstdc++ versions

The <regex> header is present but the regex implementation is incomplete and fails with regex_error exceptions in runtime for many valid patterns. So define BOOST_NO_CXX11_HDR_REGEX for it unconditionally.

See: http://thread.gmane.org/gmane.comp.lib.boost.devel/250010
Merge pull request #12 from Lastique/patch-1

Mark <regex> unusable for all libstdc++ versions