Fix bad merge of D16791 and D16767

Summary: A bad Auto-Merge caused log buffer is flushed twice. Remove the unintended one.

Test Plan: Should already be tested (the code looks the same as when I ran unit tests).

Reviewers: haobo, igor

Reviewed By: haobo

CC: ljin, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D16821

include/rocksdb/transaction_log.h

@@ -73,6 +73,12 @@ class TransactionLogIterator {
   // Can read data from a valid iterator.
   virtual bool Valid() = 0;
 
+  // IsObsolete() returns true if new log files were created. This usually
+  // means that the user needs to close the current iterator and create a new
+  // one to get the newest updates. It should happen only when mem tables are
+  // flushed.
+  virtual bool IsObsolete() = 0;
+
   // Moves the iterator to the next WriteBatch.
   // REQUIRES: Valid() to be true.
   virtual void Next() = 0;