pgsql: Revert SIGUSR1 multiplexing patch, per Tom's objection.

Log Message:
-----------
Revert SIGUSR1 multiplexing patch, per Tom's objection.

Modified Files:
--------------
pgsql/src/backend/access/transam:
twophase.c (r1.49 -> r1.50)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/twophase.c?r1=1.49&r2=1.50)
pgsql/src/backend/commands:
async.c (r1.143 -> r1.144)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/async.c?r1=1.143&r2=1.144)
pgsql/src/backend/postmaster:
autovacuum.c (r1.89 -> r1.90)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/autovacuum.c?r1=1.89&r2=1.90)
pgsql/src/backend/storage/ipc:
sinval.c (r1.87 -> r1.88)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/sinval.c?r1=1.87&r2=1.88)
sinvaladt.c (r1.75 -> r1.76)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/sinvaladt.c?r1=1.75&r2=1.76)
pgsql/src/backend/storage/lmgr:
proc.c (r1.203 -> r1.204)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/proc.c?r1=1.203&r2=1.204)
pgsql/src/backend/tcop:
postgres.c (r1.559 -> r1.560)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c?r1=1.559&r2=1.560)
pgsql/src/include/storage:
proc.h (r1.108 -> r1.109)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/proc.h?r1=1.108&r2=1.109)
sinval.h (r1.49 -> r1.50)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/sinval.h?r1=1.49&r2=1.50)
pgsql/src/include/tcop:
tcopprot.h (r1.94 -> r1.95)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/tcop/tcopprot.h?r1=1.94&r2=1.95)