tp-channel-iface.c: Make handle type read/write and constructor-only
tp-channel-iface.c: Make handle type read/write and constructor-only

This is necessary to allow GabbleRosterChannel to work for more than one handle
type.
Also fix documentation strings on handle, handle type.

20061017131837-53eee-34eb5a33c339b36ed16dfa07ca1e8aa581746d6d.gz

community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,Distrotech/telepathy-glib,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,community-ssu/telepathy-gabble,Distrotech/telepathy-glib,Distrotech/telepathy-glib,jku/telepathy-gabble,mlundblad/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble,jku/telepathy-gabble,Distrotech/telepathy-glib,mlundblad/telepathy-gabble,Distrotech/telepathy-glib,community-ssu/telepathy-gabble