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

util/coding.h

@@ -15,7 +15,7 @@
 #include <string>
 #include "port/port.h"
 
-namespace leveldb {
+namespace rocksdb {
 
 // The maximum length of a varint in bytes for 32 and 64 bits respectively.
 const unsigned int kMaxVarint32Length = 5;
@@ -129,6 +129,6 @@ extern uint64_t BitStreamGetInt(const std::string* src, size_t offset,
 extern uint64_t BitStreamGetInt(const Slice* src, size_t offset,
                                 uint32_t bits);
 
-}  // namespace leveldb
+}  // namespace rocksdb
 
 #endif  // STORAGE_LEVELDB_UTIL_CODING_H_