More cleanup of userid to be AclId rather than Oid.

src/backend/commands/cluster.c

src/backend/commands/dbcommands.c

src/backend/commands/schemacmds.c

src/backend/commands/user.c

src/backend/commands/variable.c

src/backend/executor/execMain.c

src/backend/rewrite/rewriteDefine.c

src/backend/utils/adt/acl.c

src/backend/utils/adt/ri_triggers.c

src/backend/utils/cache/lsyscache.c

src/backend/utils/fmgr/fmgr.c

src/backend/utils/init/miscinit.c

src/backend/utils/misc/superuser.c

src/include/c.h

src/include/miscadmin.h

src/include/pgstat.h

src/include/utils/acl.h