qtcreator: Update to 2.8.1
qtcreator: Make the qt package optional and introduce the QtSDK

To give the ability to use a different Qt version than the default one
(which can build 3 different times Qt Libraries if we mixed the default
one, the qtcreator one and the version including all the examples and the
docs).

Right now a developer can choose to directly install the QtSDK which
includes a "full" (developerBuild + docs + examples) Qt version and uses
it to build QtCreator.

The possibility to only install QtCreator and its previous behavior has
been kept for flexibility purposes (we do not need to force someone on the
SDK approach).
mesa: Minor fix on GL/gl.h

Apply a fix which prevented to use -DGL_GLEXT_LEGACY, -Werror and -Wundef
to be used together. This produced a build fail on any software meeting
these requirements.
Add Qt 5.1.1 and its SDK

Consider this as a first step towards the integration of Qt5 into nixpkgs,
it does not yet intends to replace Qt4 on every packages even if possible.
My goal here is to have a first derivation in common between people who
needs qt5 for development purposes.

The derivation has been written from scratch but I took care to read at the
version 4 to re-integrate some patches which are still compatible. However,
I did not had enough time to test gtkStyle and flashplayerFix as I do not
use any of them. Also, OSX users will have to do some extra work because
I do not have any mac.

Finally, as some configure flags have changed and in an hope to provide a
clear package definition before it becomes mature, I voluntary added some
flags which are default. Once every option will be mastered, we will just
have to redo a pass on qt5 configure flags and remove the ones which are
set by default.
vtk: Use the Qt libraries as an argument instead of a boolean

To prevent multiple Qt libraries when developing with a custom one, the Qt
support can now be activated by directly supplying the Qt libraries as an
argument (qtLib).

qtSDK and qtFull users/developers now just have to define an override such
as the following one in order to use it inside their development
environment:

vtk.override { qtLib = qt4SDK; };

The previous behavior is still the same for vtk and vtkWithQt4 end-users.

Change-Id: I517762d4ff7de46d32cc46e6e725fd62737caa52
Set the channel for this release
nixos/logstash: update and simplify to be fully compatible with new version
nixos/logstash: add option examples
nixos/logstash: add test
nixos/mongodb: set static uid to work with #1076
Updating gdb to 7.6.1
Merge pull request #1066 from offlinehacker/nixos/logstash/update

nixos/logstash: update and simplify to be fully compatible with new version
Leiningen: Update to 2.3.3

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Merge pull request #1182 from offlinehacker/nixos/mongodb/userfix

nixos/mongodb: set static uid to work with #1076
sane: add support for Epson snapscan scanners

The firmware file needs to be downloaded or extracted from the windows
driver file and configured in nixpkgs.config e.g.:

sane.snapscanFirmware = /firmware/esfw41.bin;
sane: tidy-up, wrap expression arguments
xsane: add optional gimp plugin support
gtk2: minor update .20 -> .22
mesa: bugfix update 9.1.6 -> .7

Thist is just for master before the official release,
x-updates has 9.2.* already.
Merge #1082: Update QtCreator to 2.8.1, add Qt 5.1.1 and QtSDK