pgsql: Fix problems with rewriter failing to set Query.hasSubLinks when

Log Message:
-----------
Fix problems with rewriter failing to set Query.hasSubLinks when inserting
a SubLink expression into a rule query.  Pre-8.1 we essentially did this
unconditionally; 8.1 tries to do it only when needed, but was missing a
couple of cases.  Per report from Kyle Bateman.  Add some regression test
cases covering this area.

Tags:
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REL8_1_STABLE

Modified Files:
--------------
    pgsql/src/backend/rewrite:
        rewriteHandler.c (r1.158.2.1 -> r1.158.2.2)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/rewrite/rewriteHandler.c.diff?r1=1.158.2.1&r2=1.158.2.2)
        rewriteManip.c (r1.92.2.1 -> r1.92.2.2)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/rewrite/rewriteManip.c.diff?r1=1.92.2.1&r2=1.92.2.2)
    pgsql/src/test/regress/expected:
        subselect.out (r1.13 -> r1.13.2.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/subselect.out.diff?r1=1.13&r2=1.13.2.1)
    pgsql/src/test/regress/sql:
        subselect.sql (r1.8 -> r1.8.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/subselect.sql.diff?r1=1.8&r2=1.8.2.1)