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
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.
Fixed the mirror:// download link for GDCM.
proot: remove self.stdenv.lib
Merge remote-tracking branch 'nixos/master' into proot

Conflicts:
	pkgs/tools/system/proot/default.nix
haskell-interpolate: update to version 0.1.0
new package: svg2tikz
pythonPackages.circus: add
python: 3.4.1 -> 3.4.2
new: gist – cli for gist.github.com
Merge branch 'master' of github.com:soenkehahn/nixpkgs

haskell-interpolate: update to version 0.1.0
ujson doesn't build on pypy
Merge pull request #4420 from flazz/master

new: gist – cli for gist.github.com
python-libvirt: update 1.2.7 -> 1.2.9

Should fix breakage due to out-of-sync version with libvirt.
add assertion to keep libvirt and libvirt-python versions in sync