fs core fixes

Please add the following 4 commits to 2.6.27-stable and 2.6.28-stable.
However, there has been a lot of change here between 2.6.28 and 2.6.29:
in particular, fs/exec.c's unsafe_exec() grew into the more complicated
check_unsafe_exec().  So applying the original patches gives too many
rejects: at the bottom is the diffstat and the combined patch required.

1
Commit: 53e9309e
Author: Hugh Dickins <hugh@veritas.com>
Date: Sat, 28 Mar 2009 23:16:03 +0000 (+0000)
Subject: compat_do_execve should unshare_files

2
Commit: e426b64c
Author: Hugh Dickins <hugh@veritas.com>
Date: Sat, 28 Mar 2009 23:20:19 +0000 (+0000)
Subject: fix setuid sometimes doesn't

3
Commit: 7c2c7d99
Author: Hugh Dickins <hugh@veritas.com>
Date: Sat, 28 Mar 2009 23:21:27 +0000 (+0000)
Subject: fix setuid sometimes wouldn't

4
Commit: f1191b50
Author: Al Viro <viro@zeniv.linux.org.uk>
Date: Mon, 30 Mar 2009 11:35:18 +0000 (-0400)
Subject: check_unsafe_exec() doesn't care about signal handlers sharing

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>