message: elle.log: fix race
  The component_stack needs protection against concurrent accesses.
diff: @@ -321,12 +321,14 @@ namespace elle
  void
  Logger::component_push(std::string const& name)
  {
  + std::lock_guard<std::recursive_mutex> lock(_mutex);
  this->_component_stack.emplace_back(name);
  }
  void
  Logger::component_pop()
  {
  + std::lock_guard<std::recursive_mutex> lock(_mutex);
  assert(!this->_component_stack.empty());
  this->_component_stack.pop_back();
  }
  @@ -373,7 +375,7 @@ namespace elle
  std::string \
  content() \
  { \
  - return Content; \
  + return boost::lexical_cast<std::string>(Content); \
  } \
  \
  virtual \
  @@ -386,10 +388,8 @@ namespace elle
  \
  elle::Plugin<Tag>::Register<Name##Tag> register_tag_##Name; \
  - ELLE_LOGGER_TAG(
  - PID, boost::lexical_cast<std::string>(elle::system::getpid()));
  - ELLE_LOGGER_TAG(
  - TID, boost::lexical_cast<std::string>(std::this_thread::get_id()));
  + ELLE_LOGGER_TAG(PID, elle::system::getpid());
  + ELLE_LOGGER_TAG(TID, std::this_thread::get_id());
  #undef ELLE_LOGGER_TAG
  }
  