* Add a param to choose storage manager
Merge branch 'master' into choose_sm
 * Fixed the bug of trying to getattr() on directory when using
 ObjectStorageManager.
 * Fixed the bug of calculating module on negative object ID for subdirectory in
 ObjectStorageManager.
 * Fixed format
Merge pull request #69 from vsfs/choose_sm

Fuse supports to choose one of two available StorageManagers