pgsql: Be a little more careful with the shift computations in QT2QTN

Log Message:
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Be a little more careful with the shift computations in QT2QTN and
makeTSQuerySign. The first of these is a live bug, on some platforms,
as per bug #5590 from John Regehr. However the consequences seem limited
because of the relatively narrow scope of use of QTNode.sign. The shift in
makeTSQuerySign is actually safe because TSQS_SIGLEN is unsigned, but it
seems like a good idea to insert an explicit cast rather than depend on that.

Modified Files:
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pgsql/src/backend/utils/adt:
tsquery_op.c (r1.9 -> r1.10)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery_op.c?r1=1.9&r2=1.10)
tsquery_util.c (r1.14 -> r1.15)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery_util.c?r1=1.14&r2=1.15)