python - be: Change error signalling of

Log Message:
-----------
Change error signalling of HeapTuple_FromTupleDescAndIterable.

Return NULL and set the Python exception instead of letting a PostgreSQL error
raise.

Also, check the results of functions to handle errors properly. Don't use
Datum_FromTypeOidAndPyObject. This will save a datumCopy in some cases.

Update callers of the function to respect the change.

Modified Files:
--------------
    be/src:
        function.c (r1.14 -> r1.15)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/function.c.diff?r1=1.14&r2=1.15)
        heaptuple.c (r1.10 -> r1.11)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/heaptuple.c.diff?r1=1.10&r2=1.11)
        query.c (r1.16 -> r1.17)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/query.c.diff?r1=1.16&r2=1.17)
        tupledesc.c (r1.11 -> r1.12)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/tupledesc.c.diff?r1=1.11&r2=1.12)
    be/src/call:
        pl.c (r1.15 -> r1.16)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/call/pl.c.diff?r1=1.15&r2=1.16)
    be/src/type:
        record.c (r1.5 -> r1.6)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/type/record.c.diff?r1=1.5&r2=1.6)