Fix corruption bug found and analyzed by dhruba@gmail.com

https://groups.google.com/d/msg/leveldb/Kc9JxuIUu5A/9P0N9RL4ar8J

src/leveldb/db/version_set.h

@@ -277,6 +277,8 @@ class VersionSet {
 
   void AppendVersion(Version* v);
 
+  bool ManifestContains(const std::string& record) const;
+
   Env* const env_;
   const std::string dbname_;
   const Options* const options_;