Imitiating buttfly in being explicitly typed

Imitiating buttfly in being explicitly typed

From there commit message
"""
    Be explicit about data types in methods that produce contact attributes
    Previously, the wrong type was returned for SimplePresence/presence.
    Until telepathy-glib 0.11.3, this was masked by the fact that TpContact
    would respond to missing or wrongly-typed information in the result of
    GetContactAttributes by falling back to a slower path. This is no longer
    done, meaning that all Butterfly contacts appear to have UNKNOWN presence.
"""