SFTP: add unit test for stat cache fix
SFTP: return $sftp object in new unit test method
SFTP: stat cache fixes
Merge pull request #409 from terrafrost/stat-cache-fix

SFTP: add unit test for stat cache fix

* terrafrost/stat-cache-fix:
  SFTP: stat cache fixes
  SFTP: return $sftp object in new unit test method
  SFTP: add unit test for stat cache fix