message: Add a backwards-compatible version of VerifyBuffer()
diff: @@ -1487,6 +1487,10 @@ class Verifier FLATBUFFERS_FINAL_CLASS {
  }
  // Verify this whole buffer, starting with root type T.
  + template<typename T> bool VerifyBuffer() {
  + return VerifyBuffer<T>(nullptr);
  + }
  +
  template<typename T> bool VerifyBuffer(const char *identifier) {
  return VerifyBufferFromStart<T>(identifier, buf_);
  }
  