[CentOS] Significant speedup of package building with mock from EPEL for RHEL 6, should definitely go in CentOS 5

The speedups in building RPM's with "mock" from the EPEL packages for
RHEL 6 are *profound*, especially if your environment is like mine and
you have thousands of user id's. The issue seems to be the handling of
"/var/log/lastlog" and similar files, which are otherwise quite large
and take significant time to compress and uncompress when laying out
new mock environments.

Karabhir, what are the odds of encouragng a switch to
http://mirrors.kernel.org/fedora-epel/6/mock-1.1.8-1.el6.src.rpm, and
backporting it to centos/5/5/extras ? It's working very well for me,
and I think it would be a helpful improvement in RPM building for both
the CentOs 5.6 and CentOS 6 efforts.