[Haskell] ANN: New Full Platform Build of Haskell Platform 8.2.1 for Mac

[Gershom B]

Thanks to some intrepid sleuthing by Albert Y. C. Lai, we realized
there was a serious problem in the full (not core) builds of HP for
Mac and Linux (not Windows).

If you've seen lots of "unusable due to shadowed dependencies" errors
on packages that came with full 8.2.1 platform installs on those
systems, this is likely why. We should have tested better and caught
this, and I'm sorry for the trouble it has caused.

I've released a new build of the full mac installer, and updated the
hash on the site. A new generic-linux build should follow soon.

Regards,
Gershom

P.s. For those interested, the technical details are at
https://github.com/haskell/haskell-platform/issues/285 -- in brief,
the platform had done builds using inplace conf files but deployed
using proper target package-conf files. This worked just fine until
the new abi-depends machinery was introduced for better computing
dependency mismatches (https://phabricator.haskell.org/D2846 is one
place to start reading about that). That new machinery then recognized
that different abis were generated for the inplace conf than the
target conf, and things went screwy. But the problem here isn't with
those changes -- it's with our inadequate testing that should have
caught when things went wrong and alerted us that we needed to step
back and fix things earlier, and the responsibility for that is all on
me.