Fix gcc warnings and errors.

Update docs.

[SVN r75284]

example/mp_float_snips.cpp

@@ -0,0 +1,28 @@
+///////////////////////////////////////////////////////////////
+//  Copyright 2011 John Maddock. 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_
+
+#include <boost/multiprecision/mp_float.hpp>
+#include <iostream>
+
+void t1()
+{
+   //[mp_float_eg
+   //=#include <boost/multiprecision/mp_float.hpp>
+
+   using namespace boost::multiprecision;
+
+   // Operations at fixed precision and full numeric_limits support:
+   mp_float_100 b = 2;
+   std::cout << std::numeric_limits<mp_float_100>::digits << std::endl;
+   std::cout << log(b) << std::endl; // print log(2)
+   //]
+}
+
+int main()
+{
+   t1();
+   return 0;
+}
+