message: Fix motor subtree being unreachable from ASCII protocol
  When get_direct_child() was invoked on an Axis Instrospectable with the
  string "motor" it instead returned an Introspectable for
  "motor_thermistor".
  This is because strncmp("motor", "motor_thermistor", 5) compares to 0.
diff: @@ -96,7 +96,7 @@ public:
  private:
  Introspectable get_direct_child(const char * name, size_t length) const {
  for (size_t i = 0; i < type_info_->property_table_length_; ++i) {
  - if (!strncmp(name, type_info_->property_table_[i].name, length)) {
  + if (!strncmp(name, type_info_->property_table_[i].name, length) && (length == strlen(type_info_->property_table_[i].name))) {
  Introspectable result;
  result.storage_ = type_info_->get_child(storage_, i);
  result.type_info_ = type_info_->property_table_[i].type_info;
  