pgsql: Add GRANT ON SEQUENCE syntax to support sequence-only

Log Message:
-----------
Add GRANT ON SEQUENCE syntax to support sequence-only permissions.
Continue to support GRANT ON [TABLE] for sequences for backward
compatibility;  issue warning for invalid sequence permissions.

[Backward compatibility warning message.]

Add USAGE permission for sequences that allows only currval() and
nextval(), not setval().

Mention object name in grant/revoke warnings because of possible
multi-object operations.

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        grant.sgml (r1.50 -> r1.51)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/grant.sgml.diff?r1=1.50&r2=1.51)
        revoke.sgml (r1.35 -> r1.36)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/revoke.sgml.diff?r1=1.35&r2=1.36)
    pgsql/src/backend/catalog:
        aclchk.c (r1.123 -> r1.124)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/aclchk.c.diff?r1=1.123&r2=1.124)
        pg_shdepend.c (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/pg_shdepend.c.diff?r1=1.6&r2=1.7)
    pgsql/src/backend/commands:
        sequence.c (r1.126 -> r1.127)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/sequence.c.diff?r1=1.126&r2=1.127)
    pgsql/src/backend/parser:
        gram.y (r2.521 -> r2.522)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y.diff?r1=2.521&r2=2.522)
    pgsql/src/backend/utils/adt:
        acl.c (r1.129 -> r1.130)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/acl.c.diff?r1=1.129&r2=1.130)
    pgsql/src/bin/pg_dump:
        dumputils.c (r1.24 -> r1.25)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/dumputils.c.diff?r1=1.24&r2=1.25)
        pg_backup_archiver.c (r1.118 -> r1.119)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_archiver.c.diff?r1=1.118&r2=1.119)
        pg_dump.c (r1.426 -> r1.427)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_dump.c.diff?r1=1.426&r2=1.427)
    pgsql/src/include/nodes:
        parsenodes.h (r1.298 -> r1.299)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/parsenodes.h.diff?r1=1.298&r2=1.299)
    pgsql/src/include/utils:
        acl.h (r1.91 -> r1.92)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/acl.h.diff?r1=1.91&r2=1.92)
    pgsql/src/test/regress/expected:
        privileges.out (r1.32 -> r1.33)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/privileges.out.diff?r1=1.32&r2=1.33)