vcard-manager: find no-op replacements with wocky_node_equal
vcard-manager: find no-op replacements with wocky_node_equal

By representing the replacement we have in mind as a WockyNode[Tree], we
don't have to reimplement the comparison.

Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble