pgsql: Replace the pg_listener-based LISTEN/NOTIFY mechanism with an

Log Message:
-----------
Replace the pg_listener-based LISTEN/NOTIFY mechanism with an in-memory queue.
In addition, add support for a "payload" string to be passed along with
each notify event.

This implementation should be significantly more efficient than the old one,
and is also more compatible with Hot Standby usage.  There is not yet any
facility for HS slaves to receive notifications generated on the master,
although such a thing is possible in future.

Joachim Wieland, reviewed by Jeff Davis; also hacked on by me.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        catalogs.sgml (r2.221 -> r2.222)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/catalogs.sgml?r1=2.221&r2=2.222)
        func.sgml (r1.503 -> r1.504)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.503&r2=1.504)
        libpq.sgml (r1.298 -> r1.299)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml?r1=1.298&r2=1.299)
        protocol.sgml (r1.80 -> r1.81)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/protocol.sgml?r1=1.80&r2=1.81)
        storage.sgml (r1.31 -> r1.32)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/storage.sgml?r1=1.31&r2=1.32)
    pgsql/doc/src/sgml/ref:
        listen.sgml (r1.23 -> r1.24)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/listen.sgml?r1=1.23&r2=1.24)
        notify.sgml (r1.31 -> r1.32)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/notify.sgml?r1=1.31&r2=1.32)
        unlisten.sgml (r1.30 -> r1.31)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/unlisten.sgml?r1=1.30&r2=1.31)
    pgsql/src/backend/access/transam:
        slru.c (r1.48 -> r1.49)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/slru.c?r1=1.48&r2=1.49)
        twophase_rmgr.c (r1.12 -> r1.13)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/twophase_rmgr.c?r1=1.12&r2=1.13)
        xact.c (r1.285 -> r1.286)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xact.c?r1=1.285&r2=1.286)
    pgsql/src/backend/catalog:
        Makefile (r1.76 -> r1.77)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/Makefile?r1=1.76&r2=1.77)
    pgsql/src/backend/commands:
        async.c (r1.150 -> r1.151)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/async.c?r1=1.150&r2=1.151)
    pgsql/src/backend/nodes:
        copyfuncs.c (r1.461 -> r1.462)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c?r1=1.461&r2=1.462)
        equalfuncs.c (r1.382 -> r1.383)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/equalfuncs.c?r1=1.382&r2=1.383)
        outfuncs.c (r1.382 -> r1.383)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c?r1=1.382&r2=1.383)
        readfuncs.c (r1.231 -> r1.232)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/readfuncs.c?r1=1.231&r2=1.232)
    pgsql/src/backend/parser:
        gram.y (r2.708 -> r2.709)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y?r1=2.708&r2=2.709)
    pgsql/src/backend/storage/ipc:
        ipci.c (r1.103 -> r1.104)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/ipci.c?r1=1.103&r2=1.104)
    pgsql/src/backend/storage/lmgr:
        lwlock.c (r1.55 -> r1.56)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lwlock.c?r1=1.55&r2=1.56)
    pgsql/src/backend/tcop:
        postgres.c (r1.589 -> r1.590)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c?r1=1.589&r2=1.590)
        utility.c (r1.332 -> r1.333)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/utility.c?r1=1.332&r2=1.333)
    pgsql/src/backend/utils/adt:
        ruleutils.c (r1.322 -> r1.323)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/ruleutils.c?r1=1.322&r2=1.323)
    pgsql/src/bin/initdb:
        initdb.c (r1.184 -> r1.185)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/initdb/initdb.c?r1=1.184&r2=1.185)
    pgsql/src/bin/psql:
        common.c (r1.143 -> r1.144)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/common.c?r1=1.143&r2=1.144)
        tab-complete.c (r1.193 -> r1.194)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/tab-complete.c?r1=1.193&r2=1.194)
    pgsql/src/include/access:
        slru.h (r1.25 -> r1.26)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/slru.h?r1=1.25&r2=1.26)
        twophase_rmgr.h (r1.11 -> r1.12)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/twophase_rmgr.h?r1=1.11&r2=1.12)
    pgsql/src/include/catalog:
        catversion.h (r1.584 -> r1.585)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.584&r2=1.585)
        pg_proc.h (r1.568 -> r1.569)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.568&r2=1.569)
    pgsql/src/include/commands:
        async.h (r1.39 -> r1.40)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/commands/async.h?r1=1.39&r2=1.40)
    pgsql/src/include/nodes:
        parsenodes.h (r1.429 -> r1.430)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/parsenodes.h?r1=1.429&r2=1.430)
    pgsql/src/include/storage:
        lwlock.h (r1.44 -> r1.45)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/lwlock.h?r1=1.44&r2=1.45)
    pgsql/src/test/regress/expected:
        guc.out (r1.9 -> r1.10)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/guc.out?r1=1.9&r2=1.10)
        sanity_check.out (r1.44 -> r1.45)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/sanity_check.out?r1=1.44&r2=1.45)
    pgsql/src/test/regress/sql:
        guc.sql (r1.8 -> r1.9)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/guc.sql?r1=1.8&r2=1.9)

Removed Files:
-------------
    pgsql/src/include/catalog:
        pg_listener.h
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_listener.h)