Implement symlinks to directories

[Sascha Hauer]

So far we only supported links to files. With this series we can
also support links to directories.

I tested all kinds of different things like:

- links to directories
- links to files
- relative links
- absolute links
- 'cd'ing to links
- links with '..' in them
- links to links

So far it works fine, but I would be surprised if there were no surprises
left in this series, so please review and test.

Sascha

----------------------------------------------------------------
Sascha Hauer (4):
      errno: Include string for ELOOP
      fs: drop path_check_prereq()
      fs: Implement links to directories
      ls: Fix showing links to directories

 commands/ls.c       |  26 ++--
 commands/readlink.c |   2 +-
 common/misc.c       |   1 +
 fs/fs.c             | 385 +++++++++++++++++++++++++++-------------------------
 include/fs.h        |   3 +-
 5 files changed, 222 insertions(+), 195 deletions(-)