Fix WaitLatchOrSocket to handle EOF on socket correctly.

When using poll(), EOF on a socket is reported with the POLLHUP not
POLLIN flag (at least on Linux).  WaitLatchOrSocket failed to check
this bit, causing it to go into a busy-wait loop if EOF occurs.
We earlier fixed the same mistake in the test for the state of the
postmaster_alive socket, but missed it for the caller-supplied socket.
Fortunately, this error is new in 9.2, since 9.1 only had a select()
based code path not a poll() based one.

src/backend/port/unix_latch.c

@@ -293,7 +293,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 			result |= WL_TIMEOUT;
 		}
 		if ((wakeEvents & WL_SOCKET_READABLE) &&
-			(pfds[0].revents & POLLIN))
+			(pfds[0].revents & (POLLIN | POLLHUP | POLLERR | POLLNVAL)))
 		{
 			/* data available in socket */
 			result |= WL_SOCKET_READABLE;