Add tests for tp_cm_message_set_message()
Add tests for tp_cm_message_set_message()

The first test destroys the delivery-echo message early. The second test
changes the delivery-echo.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib