Clarify test_message_waiting() comment.
Clarify test_message_waiting() comment.

vishwaprakashmishra/xmatrix,TouK/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,harrissoerja/vumi,harrissoerja/vumi,harrissoerja/vumi