notice and friends generate interleaved output when used concurrently

[nh2]

notice and similar functions generate interleaved output when used concurrently.

This is due to the use of hPutStrLn.

It makes writing Cabal hooks that do things in parallel a pain.

It also makes straceing cabal very annoying because it pollutes the outuput.

As a solution, we should use something like say, that prints the entire contents in one go and ensures no interleaved output.

[23Skidoo]

Sounds reasonable.