net-p2p/py-libtorrent-rasterbar: unbreak with boost 1.69

bindings/python/src/error_code.cpp:119:10: error: no matching member function for call to 'def'

.def("message", &error_category::message)
~^~~

/usr/local/include/boost/python/class.hpp:229:11: note: candidate template ignored: couldn't infer template argument 'F'

self& def(char const* name, F f)
      ^

/usr/local/include/boost/python/class.hpp:219:11: note: candidate function template not viable: requires single argument 'visitor', but 2 arguments were provided

self& def(def_visitor<Derived> const& visitor)
      ^

/usr/local/include/boost/python/class.hpp:238:11: note: candidate function template not viable: requires 3 arguments, but 2 were provided

self& def(char const* name, A1 a1, A2 const& a2)
      ^

/usr/local/include/boost/python/class.hpp:245:11: note: candidate function template not viable: requires 4 arguments, but 2 were provided

self& def(char const* name, Fn fn, A1 const& a1, A2 const& a2)
      ^

/usr/local/include/boost/python/class.hpp:261:11: note: candidate function template not viable: requires 5 arguments, but 2 were provided

self& def(char const* name, Fn fn, A1 const& a1, A2 const& a2, A3 const& a3)
      ^

bindings/python/src/error_code.cpp:127:10: error: no matching member function for call to 'def'

.def("message", &error_code::message)
~^~~

/usr/local/include/boost/python/class.hpp:229:11: note: candidate template ignored: couldn't infer template argument 'F'

self& def(char const* name, F f)
      ^

/usr/local/include/boost/python/class.hpp:219:11: note: candidate function template not viable: requires single argument 'visitor', but 2 arguments were provided

self& def(def_visitor<Derived> const& visitor)
      ^

/usr/local/include/boost/python/class.hpp:238:11: note: candidate function template not viable: requires 3 arguments, but 2 were provided

self& def(char const* name, A1 a1, A2 const& a2)
      ^

/usr/local/include/boost/python/class.hpp:245:11: note: candidate function template not viable: requires 4 arguments, but 2 were provided

self& def(char const* name, Fn fn, A1 const& a1, A2 const& a2)
      ^

/usr/local/include/boost/python/class.hpp:261:11: note: candidate function template not viable: requires 5 arguments, but 2 were provided

self& def(char const* name, Fn fn, A1 const& a1, A2 const& a2, A3 const& a3)
      ^

PR: 232525
Obtained from: upstream (libtorrent 1.1.11)