Put DiffArray in its own diffarray package

[igloo]

DiffArray currently has serious performance problems (see #2727), and is not currently being actively maintained. However, as part of the corelib array it gives the impression that it is a "blessed" library.

I propose that we split DiffArray off into its own diffarray package. This also has the advantage that it can then be maintained by a separate maintainer, if someone is interested, and it will be decoupled from GHC's major release schedule.

Deadline: 26 July (2 weeks).

[igloo]

Mailing list thread starts here:  http://www.haskell.org/pipermail/libraries/2009-July/012131.html

[igloo]

There were a couple of replies, both in favour of the proposal. Consensus: accept proposal.

[igloo]

Done. It's now in its own package, at  http://code.haskell.org/diffarray/