Add more dependencies to release.nix Haskell packages

[Chris Warburton]

The extraDeps set in release.nix tells tincify which attributes of (the
given) haskellPackages it should make available to tinc, in addition to
the usual content of Hackage.

Custom packages which depend on each other need entries added to this.

Doing this is simple, but tedious (maybe a bash script would help):

 - Try to evaluate a specific Haskell package from release.nix, e.g.
   'with import ./release.nix; stable.haskell.packages.ghc7102.mlspec'
 - Wait for it to fail (tincify runs during evaluation, not build)
 - See which dependencies Cabal complains are missing, if any.
 - Add those entries to extraDeps.
 - See if the derivation now succeeds.

The relevant failure messages look like this (mlspec is missing
mlspec-helper):

  cabal: Could not resolve dependencies:
  trying: mlspec-0.2.1.2 (user goal)
  next goal: mlspec-helper (dependency of mlspec-0.2.1.2)
  Dependency tree exhaustively searched.

Maybe write a bash loop which echoes these expressions into nix-repl,
greps aggressively to only show the cabal errors, and plays a beep after
it's done. We can then leave it going, come back when it beeps and add
any missing dependencies. Rinse and repeat, until everything works (we
hope!)