Merge changes from topic "lpdumpd"

bool Realpath(const std::string& path, std::string* result) {

  result->clear();

  char* realpath_buf = realpath(path.c_str(), nullptr);

  // realpath may exit with EINTR. Retry if so.

  char* realpath_buf = nullptr;

  do {

    realpath_buf = realpath(path.c_str(), nullptr);

  } while (realpath_buf == nullptr && errno == EINTR);

  if (realpath_buf == nullptr) {

    return false;

  }