message: Remove noop call to to_string_t
  Added in this call became ambiguous with - and turns
  out to be undeeded comletely, because this code is #ifdefed to be
  Unix-specific.
diff: @@ -297,7 +297,7 @@ private:
  if (!proxy)
  proxy = std::getenv("http_proxy");
  if (proxy)
  - c.set_proxy(web::uri(to_string_t(proxy)));
  + c.set_proxy(web::uri(proxy));
  #endif
  return c;
  