Fix integer.hpp so a compiler error is generated when the number of bits requested is greater than the max available.

Added new tests to catch this case.

[SVN r78307]

test/fail_int_exact.cpp

@@ -0,0 +1,8 @@
+//  Copyright John Maddock 2012.  
+//  Distributed under the Boost
+//  Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/integer.hpp>
+
+typedef boost::int_t<sizeof(boost::intmax_t)*CHAR_BIT + 1>::exact fail_int_exact;