If we encounter a 128KB block of zeros, try to skip to the next
data section by calling File.SeekData().
This fixes xfstests generic/285, which creates a 17TB sparse file,
and runs fsck afterwards. Without this optimization, fsck would
take ages.
OpenDir and ListXAttr skip over corrupt entries,
readFileID treats files the are too small as empty.
This improves usability in the face of corruption,
but hides the problem in a log message instead of
putting it in the return code.
Create a channel to report these corruptions to fsck
so it can report them to the user.
Also update the manpage and the changelog with the -fsck option.
Closes https://github.com/rfjakob/gocryptfs/issues/191
Most corruption cases except xattr should be covered.
With test filesystem.
The output is still pretty ugly. xattr support will
be added in the next commits.
