2.4.15

Changed

• Support more lenient usernames and group names in FTP servers
  (#507).
  Closes #506.

Fixed

• Fixed MemoryFS.move and MemoryFS.movedir not updating the name of moved
  resources, causing MemoryFS.scandir to use the old name.
  (#510).
  Closes #509.
• Make WrapFS.move and WrapFS.movedir use the delegate FS methods instead
  of fs.move functions, which was causing optimized implementation of
  movedir to be always skipped.
  (#511).