message: Fix message wording in thrown exception.
diff: @@ -2318,7 +2318,7 @@ public class MslControl {
  // If we were cancelled then return null.
  if (cancelled(rt)) return null;
  - throw new MslErrorResponseException("Error sending an automatic handshake response.", rt, e);
  + throw new MslErrorResponseException("Error receiving the message header.", rt, e);
  }
  throw e;
  } catch (final Throwable t) {
  