Have pg_receivexlog always send an invalid log position in status messages

This prevents pg_basebackup and pg_receivexlog from becoming a synchronous
standby in case 'write' is used for synchronous_commit.

Fujii Masao

src/bin/pg_basebackup/receivelog.c

@@ -307,7 +307,7 @@ ReceiveXlogStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline, char *sysi
 			char		replybuf[sizeof(StandbyReplyMessage) + 1];
 			StandbyReplyMessage *replymsg = (StandbyReplyMessage *) (replybuf + 1);
 
-			replymsg->write = blockpos;
+			replymsg->write = InvalidXLogRecPtr;
 			replymsg->flush = InvalidXLogRecPtr;
 			replymsg->apply = InvalidXLogRecPtr;
 			replymsg->sendTime = now;