title: Casablanca with boost 1.56 fails due to -Werror
body: <p>I'm trying to build <a href="https://casablanca.codeplex.com/wikipage?title=Setup%20and%20Build%20on%20Linux&amp;referringTitle=Documentation" rel="nofollow">Casablanca</a> with boost 1.56, but my build keeps failing due to boost warnings turned error by Casablanca's <code>-Werror</code> flag</p>
  
  <p>For example:</p>
  
  <pre><code>CXX=g++ BOOST_ROOT=${boost} cmake .. -DCMAKE_BUILD_TYPE=Release
  </code></pre>
  
  <p>Yields errors like (far too many to show)</p>
  
  <pre><code>/home/matt/workspace/opal2/o2linux64/Libs/boost/1.56/include/boost/system/error_code.hpp:222:36: error: ‘boost::system::errno_ecat’ defined but not used [-Werror=unused-variable]
   static const error_category &amp;  errno_ecat     = generic_category();
                                  ^
  /home/matt/workspace/opal2/o2linux64/Libs/boost/1.56/include/boost/system/error_code.hpp:223:36: error: ‘boost::system::native_ecat’ defined but not used [-Werror=unused-variable]
   static const error_category &amp;  native_ecat    = system_category();
                                  ^
  cc1plus: all warnings being treated as errors
  make[2]: *** [src/CMakeFiles/cpprest.dir/http/client/http_client_msg.cpp.o] Error 1
  </code></pre>
  
  <p>I can't seem to find any remedy on google, though I have found posts where people have built with 1.56 and don't mention disabling <code>Werror</code> in  <code>src/CMakeList.txt</code> (which incendentally seems to allow the code to build)</p>