pgsql: Support ALTER TABLESPACE name SET/RESET ( tablespace_options ).

Log Message:
-----------
Support ALTER TABLESPACE name SET/RESET ( tablespace_options ).

This patch only supports seq_page_cost and random_page_cost as parameters,
but it provides the infrastructure to scalably support many more.
In particular, we may want to add support for effective_io_concurrency,
but I'm leaving that as future work for now.

Thanks to Tom Lane for design help and Alvaro Herrera for the review.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.241 -> r1.242)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.241&r2=1.242)
    pgsql/doc/src/sgml/ref:
        alter_tablespace.sgml (r1.5 -> r1.6)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/alter_tablespace.sgml?r1=1.5&r2=1.6)
    pgsql/src/backend/access/common:
        reloptions.c (r1.30 -> r1.31)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/reloptions.c?r1=1.30&r2=1.31)
    pgsql/src/backend/catalog:
        aclchk.c (r1.159 -> r1.160)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/aclchk.c?r1=1.159&r2=1.160)
    pgsql/src/backend/commands:
        tablespace.c (r1.65 -> r1.66)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/tablespace.c?r1=1.65&r2=1.66)
    pgsql/src/backend/nodes:
        copyfuncs.c (r1.458 -> r1.459)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c?r1=1.458&r2=1.459)
        equalfuncs.c (r1.379 -> r1.380)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/equalfuncs.c?r1=1.379&r2=1.380)
        outfuncs.c (r1.379 -> r1.380)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c?r1=1.379&r2=1.380)
    pgsql/src/backend/optimizer/path:
        costsize.c (r1.213 -> r1.214)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/costsize.c?r1=1.213&r2=1.214)
    pgsql/src/backend/optimizer/util:
        plancat.c (r1.161 -> r1.162)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/plancat.c?r1=1.161&r2=1.162)
    pgsql/src/backend/parser:
        gram.y (r2.701 -> r2.702)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y?r1=2.701&r2=2.702)
    pgsql/src/backend/tcop:
        utility.c (r1.326 -> r1.327)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/utility.c?r1=1.326&r2=1.327)
    pgsql/src/backend/utils/adt:
        selfuncs.c (r1.267 -> r1.268)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/selfuncs.c?r1=1.267&r2=1.268)
    pgsql/src/backend/utils/cache:
        Makefile (r1.23 -> r1.24)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/Makefile?r1=1.23&r2=1.24)
        syscache.c (r1.123 -> r1.124)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/syscache.c?r1=1.123&r2=1.124)
    pgsql/src/bin/pg_dump:
        pg_dumpall.c (r1.129 -> r1.130)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_dumpall.c?r1=1.129&r2=1.130)
    pgsql/src/include/access:
        reloptions.h (r1.17 -> r1.18)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/reloptions.h?r1=1.17&r2=1.18)
    pgsql/src/include/catalog:
        catversion.h (r1.566 -> r1.567)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.566&r2=1.567)
        pg_tablespace.h (r1.14 -> r1.15)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_tablespace.h?r1=1.14&r2=1.15)
    pgsql/src/include/commands:
        tablespace.h (r1.21 -> r1.22)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/commands/tablespace.h?r1=1.21&r2=1.22)
    pgsql/src/include/nodes:
        nodes.h (r1.232 -> r1.233)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/nodes.h?r1=1.232&r2=1.233)
        parsenodes.h (r1.421 -> r1.422)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/parsenodes.h?r1=1.421&r2=1.422)
        relation.h (r1.182 -> r1.183)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/relation.h?r1=1.182&r2=1.183)
    pgsql/src/include/utils:
        syscache.h (r1.77 -> r1.78)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/syscache.h?r1=1.77&r2=1.78)
    pgsql/src/test/regress/input:
        tablespace.source (r1.4 -> r1.5)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/input/tablespace.source?r1=1.4&r2=1.5)
    pgsql/src/test/regress/output:
        tablespace.source (r1.8 -> r1.9)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/output/tablespace.source?r1=1.8&r2=1.9)

Added Files:
-----------
    pgsql/src/backend/utils/cache:
        spccache.c (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/spccache.c?rev=1.1&content-type=text/x-cvsweb-markup)
    pgsql/src/include/utils:
        spccache.h (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/spccache.h?rev=1.1&content-type=text/x-cvsweb-markup)