pgsql: Extend the set of frame options supported for window functions.

Log Message:
-----------
Extend the set of frame options supported for window functions.

This patch allows the frame to start from CURRENT ROW (in either RANGE or
ROWS mode), and it also adds support for ROWS n PRECEDING and ROWS n FOLLOWING
start and end points.  (RANGE value PRECEDING/FOLLOWING isn't there yet ---
the grammar works, but that's all.)

Hitoshi Harada, reviewed by Pavel Stehule

Modified Files:
--------------
    pgsql/doc/src/sgml:
        func.sgml (r1.501 -> r1.502)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.501&r2=1.502)
        syntax.sgml (r1.141 -> r1.142)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/syntax.sgml?r1=1.141&r2=1.142)
    pgsql/doc/src/sgml/ref:
        select.sgml (r1.128 -> r1.129)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/select.sgml?r1=1.128&r2=1.129)
    pgsql/src/backend/executor:
        nodeAgg.c (r1.172 -> r1.173)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeAgg.c?r1=1.172&r2=1.173)
        nodeWindowAgg.c (r1.9 -> r1.10)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeWindowAgg.c?r1=1.9&r2=1.10)
    pgsql/src/backend/nodes:
        copyfuncs.c (r1.460 -> r1.461)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c?r1=1.460&r2=1.461)
        equalfuncs.c (r1.381 -> r1.382)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/equalfuncs.c?r1=1.381&r2=1.382)
        nodeFuncs.c (r1.45 -> r1.46)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/nodeFuncs.c?r1=1.45&r2=1.46)
        outfuncs.c (r1.381 -> r1.382)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c?r1=1.381&r2=1.382)
        readfuncs.c (r1.230 -> r1.231)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/readfuncs.c?r1=1.230&r2=1.231)
    pgsql/src/backend/optimizer/plan:
        createplan.c (r1.270 -> r1.271)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/createplan.c?r1=1.270&r2=1.271)
        planner.c (r1.264 -> r1.265)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/planner.c?r1=1.264&r2=1.265)
        setrefs.c (r1.157 -> r1.158)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/setrefs.c?r1=1.157&r2=1.158)
        subselect.c (r1.158 -> r1.159)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/subselect.c?r1=1.158&r2=1.159)
    pgsql/src/backend/parser:
        gram.y (r2.707 -> r2.708)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y?r1=2.707&r2=2.708)
        parse_agg.c (r1.90 -> r1.91)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_agg.c?r1=1.90&r2=1.91)
        parse_clause.c (r1.196 -> r1.197)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_clause.c?r1=1.196&r2=1.197)
    pgsql/src/backend/utils/adt:
        ruleutils.c (r1.320 -> r1.321)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/ruleutils.c?r1=1.320&r2=1.321)
    pgsql/src/include/catalog:
        catversion.h (r1.583 -> r1.584)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.583&r2=1.584)
    pgsql/src/include/nodes:
        execnodes.h (r1.217 -> r1.218)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/execnodes.h?r1=1.217&r2=1.218)
        parsenodes.h (r1.428 -> r1.429)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/parsenodes.h?r1=1.428&r2=1.429)
        plannodes.h (r1.115 -> r1.116)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/plannodes.h?r1=1.115&r2=1.116)
    pgsql/src/include/optimizer:
        planmain.h (r1.124 -> r1.125)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/planmain.h?r1=1.124&r2=1.125)
    pgsql/src/include/parser:
        kwlist.h (r1.11 -> r1.12)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/parser/kwlist.h?r1=1.11&r2=1.12)
    pgsql/src/test/regress/expected:
        window.out (r1.4 -> r1.5)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/window.out?r1=1.4&r2=1.5)
    pgsql/src/test/regress:
        parallel_schedule (r1.60 -> r1.61)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/parallel_schedule?r1=1.60&r2=1.61)
        serial_schedule (r1.55 -> r1.56)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/serial_schedule?r1=1.55&r2=1.56)
    pgsql/src/test/regress/sql:
        window.sql (r1.4 -> r1.5)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/window.sql?r1=1.4&r2=1.5)