Fixing the cross gcc building.

gcc 4.8 added libatomic, and it has to be disabled in case of
gccCrossStageStatic, as it requires libc.
haskellPackages.amqp: Don't run tests

The tests require a running AMQP server, and fail if there isn't one running.
haskellPackages.networkMetrics: New expression
haskell-retry: jailbreak to fix build with recent versions of 'exceptions'
pass: Bump to 1.6.2.
pngcrush: update from 1.7.71 to 1.7.73.
rebar: update from 2.2.0 to 2.3.0
elixir: update from 0.13.0 to 0.13.2
linux: Update to 3.12.20
nspr: Update to 4.10.5
nss: Update to 3.16.1
firefox: Update to 29.0.1
testdisk: Enable NTFS support
blender: Make JACK support optional.
Fix a mistake on URL for fetchurl