pgsql: Treat exit code 128 (ERROR_WAIT_NO_CHILDREN) as non-fatal on

Log Message:
-----------
Treat exit code 128 (ERROR_WAIT_NO_CHILDREN) as non-fatal on Win32,
since it can happen when a process fails to start when the system
is under high load.

Per several bug reports and many peoples investigation.

Back-patch to 8.4, which is as far back as the "deadman-switch"
for shared memory access exists.

Modified Files:
--------------
    pgsql/src/backend/postmaster:
        postmaster.c (r1.615 -> r1.616)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/postmaster.c?r1=1.615&r2=1.616)