Merge branch 'hpfs' from Mikulas Patocka

Merge hpfs patches from Mikulas Patocka.

* emailed patches from Mikulas Patocka <mpatocka@artax.karlin.mff.cuni.cz>:
  hpfs: implement prefetch to improve performance
  hpfs: use mpage
  hpfs: better test for errors