message: Optimize UnescapeCString if no escaping needed
  Make the common case faster. Reduces time spent in this function when
  reading a PO file from ~3% to ~1%.
diff: @@ -119,6 +119,9 @@ inline T EscapeCString(const T& str)
  template<typename T>
  inline T UnescapeCString(const T& str)
  {
  + if (str.find('\\') == T::npos)
  + return str;
  +
  T out;
  out.reserve(str.length());
  for (auto i = str.begin(); i != str.end(); ++i)
  