Darkcoin: new package (v0.9.13.15)

Darkcoin is a privacy-centered crypto-currency.
Litecoin: Update to 0.9.3-preview5

Now Litecoin expression lives in a single file, litecoin.nix
schismtracker: new package
xlockmore: update from 5.44 to 5.45
gpgme: update from 1.5.1 to 1.5.2
gloox: update from 1.0.11 to 1.0.12
glm: update from 0.9.5.4 to 0.9.6.0
ffmpeg: update from 2.4.3 to 2.4.4
easytag: update from 2.3.1 to 2.3.2
sxiv: update git revision
mpd: update from 0.19.4 to 0.19.5
agda-TotalParserCombinators: update darcs revision

Fixes the package for new Agda version
agda-pretty: update darcs revision

Fixes the package for new Agda version
pythonPackages.sure: fix pypy and py3k builds
beret: fix hash
fix sloccount build
x86info: ignore warnings
folly: 12 -> 17, fix build
minixml: update from 2.8 to 2.9
nixos/installer: Override swap devices so tests don't fail

This patch should be reverted if either:
  - systemd fixes the multi-swapon issue.
    https://bugs.freedesktop.org/show_bug.cgi?id=86930
  - If we disable the autogeneration of swap and vfat units within
    systemd.