how to checkout proper submodules

[Kazu Yamamoto ( 山本和彦 )]

Hi,

Andreas and I found that the new IO manager is not working properly in
the current GHC head. I'm sure that it worked well at least on May 7.

We need to narrow the range of commits, so I did:

  % git checkout bb2795db36b36966697c228315ae20767c4a8753
  % git submodule update

But this does not checkout proper submodules. For instance,
libraries/base has newer commits. And of cource, building fails.

Please tell us how to checkout proper submodules against a specific
GHC tree.

--Kazu