Bug fixes and updates.

* [rar2fs #37]

  Fixed a potential memory leak when compiling against
  libunrar versions prior to 4.2.0.

* Fixed a potential memory leak in the collect_files()
  function. This function is only used when mounting
  single RAR archives which means it is rather harmless.

* Simplified code in function dir_entry_add_hash().

* Changed implementation of utimens

* [rar2fs #35]

  Fixed a problem with RAR5 stats that were incorrectly
  inherited for file reference links.