pgsql: Make CREATE/DROP/RENAME DATABASE wait a little bit to see if

Log Message:
-----------
Make CREATE/DROP/RENAME DATABASE wait a little bit to see if other backends
will exit before failing because of conflicting DB usage.  Per discussion,
this seems a good idea to help mask the fact that backend exit takes nonzero
time.  Remove a couple of thereby-obsoleted sleeps in contrib and PL
regression test sequences.

Modified Files:
--------------
    pgsql/contrib:
        Makefile (r1.76 -> r1.77)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/Makefile.diff?r1=1.76&r2=1.77)
    pgsql/src/backend/commands:
        dbcommands.c (r1.194 -> r1.195)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/dbcommands.c.diff?r1=1.194&r2=1.195)
    pgsql/src/backend/storage/ipc:
        procarray.c (r1.24 -> r1.25)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/procarray.c.diff?r1=1.24&r2=1.25)
    pgsql/src/include/storage:
        procarray.h (r1.13 -> r1.14)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/procarray.h.diff?r1=1.13&r2=1.14)
    pgsql/src/pl:
        Makefile (r1.25 -> r1.26)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/Makefile.diff?r1=1.25&r2=1.26)