Parallel installs (cabal install -j)

With cabal-install-1.16.0 parallel installs (beside other things) were introduced.

To get it, just update:

$ cabal update
$ cabal install  cabal-install Cabal

Comparison:

$ time cabal install yesod
...
Registering yesod-1.1.2

real    10m16.566s
user    7m57.422s
sys     0m22.085s

$ time ./.cabal/bin/cabal install -j4 yesod
...
Installed yesod-1.1.2

real    4m36.628s
user    13m28.371s
sys     0m37.214s