Copy/rename Writer.Strict in here
Backport to older transformers

I got the darcs HEAD, so now I have to fix type errors by comparing with
0.3.0.0.
StricterWriter: use seq for extra strictness
StricterWriter: Add to cabal file
Try (and stop) integrating StricterWriter

This would need an extra typeclass instance for lifting MonadError on
StricterWriter.

Anyway, I'm not sure this would have worked, and Tillmann fixed this
otherwise. So aborting here.