Currently we start the slow-path if the feature has not been set after GetContactAttributes has returned. We should rather only start it if the iface is not listed in ContactAttributeInterfaces.
http://git.collabora.co.uk/?p=user/cassidy/telepathy-glib;a=shortlog;h=refs/heads/slow-path-27695
I'd prefer the helper function to be called contacts_context_supports_iface. With that change, review+.
I amend the commit and merged it. Will be in 0.11.3
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