Change namespace from leveldb to rocksdb

Summary:
Change namespace from leveldb to rocksdb. This allows a single
application to link in open-source leveldb code as well as
rocksdb code into the same process.

Test Plan: compile rocksdb

Reviewers: emayanke

Reviewed By: emayanke

CC: leveldb

Differential Revision: https://reviews.facebook.net/D13287

table/iterator_wrapper.h

@@ -5,7 +5,7 @@
 #ifndef STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
 #define STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
 
-namespace leveldb {
+namespace rocksdb {
 
 // A internal wrapper class with an interface similar to Iterator that
 // caches the valid() and key() results for an underlying iterator.
@@ -58,6 +58,6 @@ class IteratorWrapper {
   Slice key_;
 };
 
-}  // namespace leveldb
+}  // namespace rocksdb
 
 #endif  // STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_