TpBaseContactList: rename queued_requests to channel_requests
TpBaseContactList: rename queued_requests to channel_requests

When implementing the new D-Bus API, we'll also need a queue of structs
representing GetContactListAttribute calls, so we should be specific about
which requests are queued here.

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