tp_text_channel_supports_message_type: rename arg to message_type to match the name in the declaration
tp_text_channel_supports_message_type: rename arg to message_type to match the name in the declaration

This makes gtk-doc happy.

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