Add ReadOptions to TransactionLogIterator.

Summary:
Add an optional input parameter ReadOptions to DB::GetUpdateSince(),
which allows the verification of checksums to be disabled by setting
ReadOptions::verify_checksums to false.

Test Plan: Tests are done off-line and will not be included in the regular unit test.

Reviewers: igor

Reviewed By: igor

CC: leveldb, xjin, dhruba

Differential Revision: https://reviews.facebook.net/D16305

include/utilities/stackable_db.h

@@ -152,10 +152,10 @@ class StackableDB : public DB {
     return db_->GetPropertiesOfAllTables(props);
   }
 
-  virtual Status GetUpdatesSince(SequenceNumber seq_number,
-                                 unique_ptr<TransactionLogIterator>* iter)
-    override {
-      return db_->GetUpdatesSince(seq_number, iter);
+  virtual Status GetUpdatesSince(
+      SequenceNumber seq_number, unique_ptr<TransactionLogIterator>* iter,
+      const TransactionLogIterator::ReadOptions& read_options) override {
+    return db_->GetUpdatesSince(seq_number, iter, read_options);
   }
 
  protected: