Proposal: POSIX process group API reform

[Favonia]

I am proposing a POSIX process group API change in order to
(1) make ProcessGroupID a newtype of CPid, and
(2) make it possible to query the process group of an existing process.

The motivation is that currently there is no way to query a process
group of an existing process, but it seems needed for a proper
implementation for ticket #3994. Also it seems nice if the compiler
can do distinguish ProcessGroupID from ProcessID, just like Fd from
CInt.

The full proposal is at the wiki page
http://www.haskell.org/haskellwiki/POSIX_process_groups_reform_proposal
. The patches and test cases are all attached in the ticket
http://hackage.haskell.org/trac/ghc/ticket/5167 .

For backward compatibility the current patches preserv the current
implementation if possible. In contrast the proposal on the wiki
suggests a more aggressive reformation.

Thanks,
Favonia

PS: Sorry but the patch to the package base is not fully tested, as I
have not figured out the correct way to compile package base (even
without the patch). However the patch to the package unix should work
independently of the patch to the package base.