Plugins won't load compiled object file on nix using ghc 7.8.4.

> gitit: :
> cannot find normal object file ‘wikistatic/private/plugins/GnuPlot.dyn_o’
> while linking an interpreted expression
> Gitit server closed.

Was working perfectly on nix using ghc 7.6.x.

Now, here is the situation, after the plugin load stage, I can find a `*.o` and a
`.hi` alongside the plugin's `*.hs`. However, the message seems to refer to
a missing `*.dyn_o`.

To me, it look like a problem with the recent use of dynamic libraries for ghc
packages. It may be a GHC issue, however we will have to circumvent this.

Someone has an idea?