mock and sha256 rpms

[Mike McLean]

If you use mock for building, then you may be in the position of having 
the main system rpm use sha256 checksums (e.g. on F11) but create 
chroots that contain an older rpm that does not.

If you create a source rpm using the newer rpm and pass it to mock to 
build in a chroot with an older rpm, you will get an error like the 
following:
> DEBUG util.py:256:  error: unpacking of archive failed on file /builddir/build/SOURCES/INIT.2008-02-02.tgz;4a1e5c21: cpio: MD5 sum mismatch
> DEBUG util.py:319:  Child returncode was: 1

I think the simplest way to work around this is to have mock pass 
--nomd5 to rpm when installing the srpm in the chroot.

Of course, this is dropping an integrity check, so could possibly add a 
check outside the chroot to verify this data. Granted, I'm not sure what 
the best way to do that is.

Thoughts? Concerns?