Announce drop of support for Python < 2.6.
Don't build extensions for Python 2.3-2.5.

We only officially support Python 2.6-2.7 now,
and they probably didn't work properly anyway.
We should always have Python 2.6 or greater now.
Note 64-bit and Python >= 2.6 support.
Pull in EPEL Python 2.6 package on RHEL 5.