Upgrade VirtualBox Guest Additions to 4.2.6
virtualbox: Update to new upstream version 4.2.6.

Fortunately this time the upstream package was packaged correctly and we no
longer need the patch to remove the reference to the fa_IR locale.

In addition we need to add lvm2 to dependencies because VirtualBox now requires
libdevmapper with its default configuration. We could disable it but in order to
gain DM support I think it's necessary and at least could avoid some confusion
from users if it's not working "out of the box" :-)

This is a bugfix release, upstream changes are:

 * VMM: don't inject stale VT-x events to prevent crashes after VM reset
 * VMM: workaround for buggy BIOSes which enable MONITOR only for certain CPUs
 * GUI: fixed trimming of anti-aliased text in details-view element headers
 * GUI: fixed create-settings-file-alias functionality on Mac hosts
 * GUI: fixed take-guest-screenshot functionality on Windows hosts
 * GUI: several minor fixes, including palette fixes
 * GUI: fixed Windows 2012 OS type
 * GUI: allow to terminate the VM even if VBoxSVC crashed
 * API: fixed cancelling of snapshots, previously this could lead to
        inconsistent VM configs
 * API: fixed identifying disk images by UUID
 * 3D Support: several fixes
 * VRDP: fixed occasional crash with external authentication
 * VGA: fix for double scan text modes
 * USB: fixed invalid pending request count at the time of service of DEVICE
        POWER requests (Windows hosts only)
 * USB keyboard: Korean keyboard workaround
 * Storage: fixed hang with QCOW images and asynchronous I/O enabled
 * Storage: fixed hang with newer VHD images
 * Storage: actually write the non-rotational flag to the VM settings (4.2.0
            regression)
 * Virtio-net: fixed the problem with network statistics counters in Session
               Information dialog (GUI)
 * Metrics: introduced network rate and disk usage metrics
 * Metrics: fixed a crash under certain conditions on Solaris hosts
 * BIOS: fix for El Torito
 * Shared Folders: if the host folder of a shared folder mapping does not exist,
                   keep it active but mark it as invalid to prevent inconsistent
                   saved states
 * VBoxManage: fixed converting disks from raw images
 * VBoxManage: show snapshot description in the VM or snapshot information
 * VBoxManage: make implicit opening of media consistent in all places dealing
               with media
 * VBoxManage: the iSCSI initiator name was not stored in the settings file when
               doing storageattach
 * VBoxManage: metrics collect now properly handles 'CPU/MHz' and
               'Net/*/LinkSpeed' metrics
 * VBoxManage: changing the image UUID or parent UUID as part of storageattach
               works now in all safe cases
 * VBoxManage: introduced storageattach --medium additions as a shortcut to
               mount the additions image
 * OVF: fixed importing OVF files cerated by recent VMware products
 * Linux hosts / Bridged Networking: fixed the problem with leaking connections
                                     in conntrack
 * Linux Additions: added support for ConsoleKit sessions in the vminfo service
                    of VBoxService
 * Linux Additions: don't crash during remount under certain conditions
 * Linux/Solaris Additions: fixed guest memory metrics collection
 * Solaris hosts: added a dependency to ensure that the user directories are
                  reachable when starting VBox services
 * Windows host installer: integrated user-contributed translations, thanks to
                           all contributors!
 * Windows Additions: fixed auto-logon installation for Windows 8
 * Windows Additions: don't fail if the shared folders host service is not
                      available
 * Windows Additions: fixed Guest Additions startup on Windows 2000 guests
 * Windows Additions: auto-resize fixes for Windows 8 guests

Upstream changelist with bug ids can be found here:

https://www.virtualbox.org/wiki/Changelog

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Merge pull request #239: VirtualBox guest update.

So, a VirtualBox update is best accompanied by the corresponding update of the
guest additions.

Thanks @dysinger for the contribution.
chromium: Add pulse_audio_fix.patch to nixpkgs.

The patch previously was fetched from an Arch Linux contributor but is no longer
available there anymore. So, this is only an intermediate fix until channels get
updated (very soon I hope, even though chromium 25 could get quite messy).

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
xf86-video-nouveau: Add pixman to buildInputs.

Well, either this build is only broken on my system or noone actually uses
nouveau? Even when looking into the source tree it seems to require pixman, so I
suppose it didn't work for anyone prior to this commit.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>