Fixes #433.

small documentation fixes

'... another level of indirection not shown in the figure above ...'
but in the 'user-environments.png' figure there is '~/.nix-profile'.
the figure was updated with the commit: f982df3c on Mar 16, 2005.

  '... when when ...' -> '... when ...'

Let's not just improve the error message itself, but also the behaviour
to actually work around the ntfs-3g symlink bug. If the readlink() call
returns a smaller size than the stat() call, this really isn't a problem
even if the symlink target really has changed between the calls.

So if stat() reports the size for the absolute path, it's most likely
that the relative path is smaller and thus it should also work for file
system bugs as mentioned in 93002d69fc58c2b71e2dfad202139230c630c53a.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Tested-by: John Ericson <Ericson2314@Yahoo.com>

A message like "error: reading symbolic link `...' : Success" really is
quite confusing, so let's not indicate "success" but rather point out
the real issue.

We could also limit the check of this to just check for non-negative
values, but this would introduce a race condition between stat() and
readlink() if the link target changes between those two calls, thus
leading to a buffer overflow vulnerability.

Reported by @Ericson2314 on IRC. Happened due to a possible ntfs-3g bug
where a relative symlink returned the absolute path (st_)size in stat()
while readlink() returned the relative size.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Tested-by: John Ericson <Ericson2314@Yahoo.com>

For some reason, docbook-xsl doesn't render edition.

See NixOS/nixpkgs@9245516

Add exe, dll to .gitignore

It's outdated and better covered in the Nixpkgs manual.

http://hydra.nixos.org/build/17894500

Closes #415.

Also, make it more robust against incorrent SSL_CERT_FILE values.

http://hydra.nixos.org/build/17862041