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.

Modified Files:
--------------
    pgsql/src/backend/rewrite:
        rewriteHandler.c (r1.159 -> r1.160)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/rewrite/rewriteHandler.c.diff?r1=1.159&r2=1.160)
        rewriteManip.c (r1.93 -> r1.94)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/rewrite/rewriteManip.c.diff?r1=1.93&r2=1.94)
    pgsql/src/test/regress/expected:
        subselect.out (r1.13 -> r1.14)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/subselect.out.diff?r1=1.13&r2=1.14)
    pgsql/src/test/regress/sql:
        subselect.sql (r1.8 -> r1.9)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/subselect.sql.diff?r1=1.8&r2=1.9)