Merge branch 'fix-unmapped-word-at-a-time'

Jana Saout confirmed that this fixes the page faults he saw.

His problem was triggered by ocfs2 and autofs symlink lookups, where the
symlink allocation was at the end of a page.  But the deeper reason
seems to be the use of Xen-PV, which is what then causes him to have all
these unmapped pages, which is what then makes it a problem when the
unaligned word-at-a-time code fetches data past the end of a page.

* fix-unmapped-word-at-a-time:
  vfs: make word-at-a-time accesses handle a non-existing page