applications/audio/jack-rack: New nixpkg.
xfdesktop: minor update
jbig2dec: fix download URI
graphviz: fix vimdot program

vimdot doesn't work at the moment because one of its dependencies,
'which', is missing; vimdot fails to find gvim or vim and aborts.
Instead of adding a dependency on 'which', replace it with the POSIX
command 'command -v'.
xfce4-power-manager: update this forgotten package
git: link binaries with libgcc_s.so to ensure pthread_cancel() works
haskell-blaze-html: update to version 0.6.1.1
haskell-blaze-markup: update to version 0.5.1.5
haskell-citeproc-hs: update to version 0.3.8
haskell-distributive: update to version 0.3.1
haskell-gitit: update to version 0.10.3
haskell-hakyll: update to version 4.2.1.1
haskell-haskell-src-meta: update to version 0.6.0.2
haskell-pandoc: update to version 1.11
haskell-publicsuffixlist: update to version 0.0.4
haskell-stylish-haskell: update to version 0.5.6.1
haskell-void: update to version 0.5.12
haskell-wl-pprint-extras: update to version 3.4
haskell-wl-pprint-terminfo: update to version 3.6
haskell-yst: update to version 0.3.1.1