It is now in its own diffarray package

As well as checking that offset we are reading is actually inside the
array, we now also check that it is "in range" as defined by the Ix
instance. This fixes confusing behaviour (#2120) and improves some error
messages (#2669).

These instances aren't orphans; they'll be available if Foldable or
Traversable are.  They shouldn't be here because then they'd leak the
instances in Control.Monad.Instances into the Haskell 98 module Array.

Now that orphan warnings obey -Werror, we must suppress them when
they occur.

I'd prefer that these three modules didn't have orphans; Ian is going
to look into this.

These are no longer needed, now that Prelude is in a different package

Specify the build-type and min cabal-version.
Don't have Data.Array in both exposed-modules on both sides of a
conditional, just make it unconditional.
Stop using -fglasgow-exts and specify all the extensions explicitly.
Some extensions are conditional on non-nhc98 and some are ghc-specific.

The real reason to not import Control.Applicative is that it exports
the non-H98 instance Functor ((->) a) and it is important for
Data.Array to not re-export that because the H98 Array module
re-exports bits of Data.Array and it is vital that we do not export
non-H98 instances from a module specified in H98.