Bump mpv to 0.3.8
Add subtitle option for ffmpeg.
ghc-head: update snapshot to 7.9.20140430 (and download the tarball from Debian)

https://github.com/NixOS/nixpkgs/pull/2480
Bootstrap ghc-head with GHC 7.6.3 to see if that solves our weird compiler errors:

  compiler/simplCore/CoreMonad.lhs:835:10:
      Non type-variable argument in the constraint: MonadPlus IO
      (Use -XFlexibleContexts to permit this)
      In the context: (MonadPlus IO)
      While checking an instance declaration
      In the instance declaration for `A.Alternative CoreM'

  compiler/simplCore/CoreMonad.lhs:841:10:
      Non type-variable argument in the constraint: MonadPlus IO
      (Use -XFlexibleContexts to permit this)
      In the context: (MonadPlus IO)
      While checking an instance declaration
      In the instance declaration for `MonadPlus CoreM'
haskell-xmonad-contrib: update to version 0.11.3
haskell-Hipmunk: update to version 5.2.0.14
haskell-JuicyPixels: update to version 3.1.5.1
haskell-ghc-events: update to version 0.4.3.0
haskell-github: update to version 0.8
haskell-libmpd: update to version 0.8.0.3
haskell-logging: update to version 1.4.1
haskell-monad-extras: update to version 0.5.8
haskell-pcre-light: update to version 0.4.0.2
haskell-stringable: update to version 0.1.3
haskell-HaRe: update to version 0.7.2.3
haskell-hslogger: update to version 1.2.4
haskell-threadscope: update to version 0.2.3
haskell-attoparsec: update to version 0.11.3.0
haskell-unordered-containers: update to version 0.2.4.0
haskell-fgl: add version 5.5.0.1