timeout of pg_receivexlog --status-interval

Hi,

At 1047 line of receivelog.c:CopyStreamPoll(), we set NULL to
timeoutptr variable.
if the value of timeoutprt is set NULL then the process will wait
until can read socket using by select() function as following.

if (timeout_ms < 0)
timeoutptr = NULL;
else
{
timeout.tv_sec = timeout_ms / 1000L;
timeout.tv_usec = (timeout_ms % 1000L) * 1000L;
timeoutptr = &timeout;
}

ret = select(PQsocket(conn) + 1, &input_mask, NULL, NULL, timeoutptr);

But the 1047 line of receivelog.c is never executed because the value
of timeout_ms is NOT allowed less than 0 at CopyStreamReceive which is
only one function calls CopyStreamPoll().
The currently code, if we specify -s to 0 then CopyStreamPoll()
function is never called.
And the pg_receivexlog will be execute PQgetCopyData() and failed, in
succession.

I think that it is contradiction, and should execute select() function
with NULL of fourth argument.
the attached patch allows to execute select() with NULL, i.g.,
pg_receivexlog.c will wait until can read socket without timeout, if
-s is specified to 0.

Regards,
-------
Sawada Masahiko