Revert changes to develop branch.

Simplest way to merge to master.

include/boost/functional/hash/detail/float_functions.hpp

@@ -7,12 +7,12 @@
 #define BOOST_FUNCTIONAL_HASH_DETAIL_FLOAT_FUNCTIONS_HPP
 
 #include <boost/config.hpp>
-#if defined(BOOST_HAS_PRAGMA_ONCE)
-#pragma once
-#endif
-
 #include <boost/config/no_tr1/cmath.hpp>
 
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
 // Set BOOST_HASH_CONFORMANT_FLOATS to 1 for libraries known to have
 // sufficiently good floating point support to not require any
 // workarounds.