pgsql: Get rid of the separate EState for subplans, and just let them

Log Message:
-----------
Get rid of the separate EState for subplans, and just let them share the
parent query's EState.  Now that there's a single flat rangetable for both
the main plan and subplans, there's no need anymore for a separate EState,
and removing it allows cleaning up some crufty code in nodeSubplan.c and
nodeSubqueryscan.c.  Should be a tad faster too, although any difference
will probably be hard to measure.  This is the last bit of subsidiary
mop-up work from changing to a flat rangetable.

Modified Files:
--------------
    pgsql/src/backend/executor:
        execMain.c (r1.288 -> r1.289)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execMain.c.diff?r1=1.288&r2=1.289)
        execProcnode.c (r1.60 -> r1.61)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execProcnode.c.diff?r1=1.60&r2=1.61)
        execQual.c (r1.213 -> r1.214)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execQual.c.diff?r1=1.213&r2=1.214)
        execUtils.c (r1.146 -> r1.147)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execUtils.c.diff?r1=1.146&r2=1.147)
        nodeSubplan.c (r1.86 -> r1.87)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeSubplan.c.diff?r1=1.86&r2=1.87)
        nodeSubqueryscan.c (r1.36 -> r1.37)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeSubqueryscan.c.diff?r1=1.36&r2=1.37)
    pgsql/src/backend/nodes:
        copyfuncs.c (r1.368 -> r1.369)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c.diff?r1=1.368&r2=1.369)
        outfuncs.c (r1.301 -> r1.302)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c.diff?r1=1.301&r2=1.302)
    pgsql/src/backend/optimizer/plan:
        planner.c (r1.215 -> r1.216)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/planner.c.diff?r1=1.215&r2=1.216)
        subselect.c (r1.121 -> r1.122)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/subselect.c.diff?r1=1.121&r2=1.122)
    pgsql/src/include/executor:
        executor.h (r1.138 -> r1.139)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/executor.h.diff?r1=1.138&r2=1.139)
        nodeSubplan.h (r1.25 -> r1.26)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/nodeSubplan.h.diff?r1=1.25&r2=1.26)
    pgsql/src/include/nodes:
        execnodes.h (r1.169 -> r1.170)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/execnodes.h.diff?r1=1.169&r2=1.170)
        plannodes.h (r1.92 -> r1.93)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/plannodes.h.diff?r1=1.92&r2=1.93)
        relation.h (r1.138 -> r1.139)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/relation.h.diff?r1=1.138&r2=1.139)