Sanity check on Open

Summary:
Everytime a client opens a DB, we do a sanity check that:
* checks the existance of all the necessary files
* verifies that file sizes are correct

Some of the code was stolen from https://reviews.facebook.net/D16935

Test Plan: added a unit test

Reviewers: dhruba, haobo, sdong

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17097

include/rocksdb/db.h

@@ -91,14 +91,6 @@ class DB {
       const std::string& name, DB** dbptr,
       bool error_if_log_file_exist = false);
 
-  // Check the consistency of live files' metadata.
-  // It will return Corruption Status when a file in manifest
-  // doesn't actually exist or doesn't match the actual file size.
-  // Note: This call should be invoked only when the database is
-  // not already open and serving data.
-  static Status CheckConsistency(const Options& options,
-      const std::string& name);
-
   DB() { }
   virtual ~DB();