Repo permissions broken

[Simon Marlow]

I tried and failed to push to the testsuite repo today.

$ git push
Counting objects: 12, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (7/7), done.
Writing objects: 100% (7/7), 695 bytes, done.
Total 7 (delta 5), reused 0 (delta 0)
error: insufficient permission for adding an object to repository 
database ./objects

fatal: failed to write object
error: unpack failed: unpack-objects abnormal exit
To simonmar at darcs.haskell.org:/srv/darcs/testsuite.git
  ! [remote rejected] master -> master (n/a (unpacker error))
error: failed to push some refs to 
'simonmar at darcs.haskell.org:/srv/darcs/testsuite.git'

It looks like we're not setting group write permission correctly after 
commits:

simonmar at ghc:/home/darcs/testsuite.git/objects$ ls -l
total 136
drwxr-sr-x 2 ezyang   darcs 4096 Jul 20 22:53 02
drwxr-sr-x 2 simonmar darcs 4096 Jul 22 09:51 0a
drwxr-sr-x 2 ezyang   darcs 4096 Jul 20 18:13 0f

I vaguely recall that we used to do this with a post-commit hook to do a 
'chmod g+w -R' on the tree.  Could someone look into this please?

Cheers,
	Simon