nixos: Add option services.cron.cronFiles

This allows you to configure extra files that should be appended to your
crontab. Implemented by writing to /etc/crontab when the cron service starts.
Would be nicer to use a cron that supports /etc/cron.d but that would require
us to patch vixie-cron.
stumpwm: update and refactoring

This commit updates the stumpwm to version 0.9.8. Futhermore, it
refactors the expression quite a lot:

* stumpwm has been moved from lisp modules to window-managers.
* stumpwm has been added to the window managers NixOS knows about, this
  enables the user to add stumpwm as a default window manager in his
  NixOS configuration like with Xmonad or i3.
* the package has been split into stumpwm and stumpwmContrib. This is
  due to the fact that development of stumpwm and its extension modules
  has been split into two repositories. As of today, the release is the
  last one before this split. This split into two packages only reflect
  those upcoming upstream changes already.

It is planned to make the addition of the extension modules voluntarily,
like with Xmonads option "enableContribAndExtras". Furthermore it might
be possible to add an option to compile stumpwm with clisp instead of
sbcl.
stumpwm: removed from lisp-packages.
logstash service improvements

* add logstash-contrib plugins package
* add additional options to the logstash service
udisks: update from 1.0.4 to 1.0.5
update fish shell
traceroute: depends on linux headers.
Nixpkgs manual: Mention xz support

Issue #4393.
proot: User-space implementation of chroot, mount --bind and binfmt_misc
Add claws-mail and libetpan.

Adds Nix expressions for claws-mail (http://www.claws-mail.org) and a
dependency that is not already in the tree, libetpan
(http://www.etpan.org/libetpan.html).

The Claws expression has flags for toggling the build of various plugins.
Added the grassroots DICOM library.
Added the dlib machine learning library.
sweethome3d: add icon to desktop file
Fixed the mirror:// download link for GDCM.
ocrad: update from 0.23 to 0.24
add redmine package
nixos: add redmine service
proot: remove unnecessary phases
Merge branch 'nixos-cronfiles' of git://github.com/rickynils/nixpkgs

nixos: Add option services.cron.cronFiles
Merge pull request #4406 from wavewave/proot

proot: User-space implementation of chroot, mount --bind and binfmt_misc