qt: make docs, demos and examples optionnaly available

As the only option before was to don't include them at all.
qtcreator: Update to 2.7.1 and improvements (merge #579)

- Qt is now directly overriden in QtCreator's definition.
- qt48Full can be used in a development environment to enable access to
docs demos and examples.

NOTE: It may be required to remove older configuration files located in
~/.config/QtProject and at ~/.config/Trolltech.conf to reconfigure
qtcreator with the correct paths. I have found /nix/store/... paths in the
following files:
$HOME/.config/QtProject/qtcreator/toolchains.xml
$HOME/.config/QtProject/qtcreator/qtversion.xml
$HOME/.config/QtProject/qtcreator/helpcollection.qhc

At the first launch, be sure to check your qtcreator's configuration by
selecting Tools->Options. The most important parts are the Kits and
QtVersion tabs located in the Build & Run section.
release-haskell: drop packages that are broken in HP 2013.2.0.0

The following packages don't compile with recent versions of GHC and
seem unmaintained, too: distributedProcess, Ebnf2ps, epic, HFuse,
Hipmunk, hspread, ltk, multiset, strictConcurrency, vacuumCairo, wxcore,
wx, wxdirect.
haskell-repa-examples: update to version 3.2.3.2
haskell-repa: update to version 3.2.3.3
haskell-shakespeare-i18n: update to version 1.0.0.3
haskell-stm-chans: update to version 3.0.0
haskell-stm-conduit: update to version 2.1.0
haskell-cabal2nix: update to version 1.50
haskell-yesod-platform: add version 1.2.0.1
release.nix, release-small.nix: build atlas library on Hydra

This puppy takes several hours to compile, being able to download that
package in binary form is really valuable.
iw: update to 3.10.

The newer, the better.
youtube-dl: without pandoc on non-pc