Initial commit of v4 of boost.regex on regex-4 branch

[SVN r18128]

include/boost/regex.hpp

@@ -28,7 +28,15 @@
 #ifndef BOOST_RE_REGEX_HPP
 #define BOOST_RE_REGEX_HPP
 
+#ifndef BOOST_REGEX_CONFIG_HPP
+#include <boost/regex/config.hpp>
+#endif
+
+#ifdef BOOST_REGEX_V3
 #include <boost/regex/v3/regex.hpp>
+#else
+#include <boost/regex/v4/regex.hpp>
+#endif
 
 #endif  // include