pgsql: Add an "argisrow" field to NullTest nodes, following a plan made

Log Message:
-----------
Add an "argisrow" field to NullTest nodes, following a plan made way back in
8.2beta but never carried out.  This avoids repetitive tests of whether the
argument is of scalar or composite type.  Also, be a bit more paranoid about
composite arguments in some places where we previously weren't checking.

Modified Files:
--------------
    pgsql/src/backend/executor:
        execQual.c (r1.257 -> r1.258)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execQual.c?r1=1.257&r2=1.258)
    pgsql/src/backend/nodes:
        copyfuncs.c (r1.456 -> r1.457)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c?r1=1.456&r2=1.457)
        equalfuncs.c (r1.377 -> r1.378)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/equalfuncs.c?r1=1.377&r2=1.378)
        outfuncs.c (r1.377 -> r1.378)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c?r1=1.377&r2=1.378)
        readfuncs.c (r1.228 -> r1.229)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/readfuncs.c?r1=1.228&r2=1.229)
    pgsql/src/backend/optimizer/path:
        indxpath.c (r1.243 -> r1.244)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/indxpath.c?r1=1.243&r2=1.244)
    pgsql/src/backend/optimizer/plan:
        planagg.c (r1.48 -> r1.49)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/planagg.c?r1=1.48&r2=1.49)
    pgsql/src/backend/optimizer/util:
        clauses.c (r1.281 -> r1.282)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/clauses.c?r1=1.281&r2=1.282)
        plancat.c (r1.159 -> r1.160)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/plancat.c?r1=1.159&r2=1.160)
        predtest.c (r1.28 -> r1.29)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/predtest.c?r1=1.28&r2=1.29)
    pgsql/src/backend/parser:
        parse_expr.c (r1.251 -> r1.252)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_expr.c?r1=1.251&r2=1.252)
    pgsql/src/include/catalog:
        catversion.h (r1.563 -> r1.564)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.563&r2=1.564)
    pgsql/src/include/nodes:
        execnodes.h (r1.214 -> r1.215)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/execnodes.h?r1=1.214&r2=1.215)
        primnodes.h (r1.152 -> r1.153)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/primnodes.h?r1=1.152&r2=1.153)