[web/views/rdf] Take the second element of XY equivalent for non final relation When given a Yams snippet of the form `<etype> <rtype>` ``xy.xeq()`` will return the XML snippet equivalent to this relation in the form of a tuple `(subject, rtype, object)` so ``item`` will always be a tuple here. In fact, the correct code appears just a few lines above (around line 88) for final relations so I guess this is a copy-paste mistake. Closes #4745929.

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if repo.system_source.dbdriver == 'postgres':

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    sql('ALTER TABLE appears ADD COLUMN weight float')

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    sql('UPDATE appears SET weight=1.0 ')