Fix Visual C++ warning in hash. Refs #8568.

I changed this a little from the patch on #8568. I moved the pragmas to the
start and end of the file because I don't like to little the body of the code
with them (this does mean I've disabled a potentially useful warning, but the
code is pretty stable nowadays).

I also removed the version checks, as the warning should be present in later
versions.


[SVN r85248]

include/boost/functional/hash/hash.hpp

@@ -27,6 +27,13 @@
 #include <typeindex>
 #endif
 
+#if defined(BOOST_MSVC)
+#pragma warning(push)
+#pragma warning(disable:6295) // Ill-defined for-loop : 'unsigned int' values
+                              // are always of range '0' to '4294967295'.
+                              // Loop executes infinitely.
+#endif
+
 #if BOOST_WORKAROUND(__GNUC__, < 3) \
     && !defined(__SGI_STL_PORT) && !defined(_STLPORT_VERSION)
 #define BOOST_HASH_CHAR_TRAITS string_char_traits
@@ -518,6 +525,10 @@ namespace boost
 
 #undef BOOST_HASH_CHAR_TRAITS
 
+#if defined(BOOST_MSVC)
+#pragma warning(pop)
+#endif
+
 #endif // BOOST_FUNCTIONAL_HASH_HASH_HPP
 
 // Include this outside of the include guards in case the file is included