Leave it to 'git submodule init/update'

Based on a patch from Thorkil Naur.

As per a request from Simon PJ, I wrote up a formalism of the core
language in GHC, System FC. The writeup lives in docs/core-spec.
I also added comments to a number of files dealing with the core
language reminding authors to update the formalism when updating the
code. In the next commit will be a README file in docs/core-spec
with more details of how to do this.

The default behavior of :info is to show only those instances of
for a type, where all relevant type constructor names are in scope.
This keeps down the number of instances shown to the user.

In some cases, it is nice to be able to see all instances for a type.
This patch implements this with the :info! command.

Based on patch from Peter Trommler:

    From 293495d40f62e691520331a41c6d85d82e120169 Mon Sep 17 00:00:00 2001
    From: Peter Trommler <ptrommler@acm.org>
    Date: Sun, 21 Oct 2012 18:47:01 +0200
    Subject: [PATCH] Add configure option to use system provided libffi This
     fixes track # 5743 and #4496.

It looks like it would fail anyway, as it 'show'ed its argument before
passing it on to printf.

Fixes Trac #7404

Trac #7410 pointed out a terrible error message, which is
much improved by this patch.

See Note [Newtype constructor usage in foreign declarations] in TcForeign.
It's quite non-trivial to say which newtype constructor are used in
foreign import/export declarations, and I had to do a bit of refactoring
to achieve it.  (Say hello to the X5 bus from Oxford to Cambridge.)
It's a bit tiresome, with some more plumbing, but not hard.

Trac #7048 triggered this change.

Fixes Trac #7451. See Note [Kind Constraint and kind *] in Kind.lhs.

The workaround described in note [darwin-x86-pic] applies to Darwin/PPC too.

This reverts commit eb5196c4.

For some reason it didn't work, and I don't have time to look into it
right now.