Add PUIAS (aka. Springdale) repo (for CMake 2.8)

PUIAS (Princeton University Institute for Advanced Studies) seems to be
the only RHEL-derived distribution that provides CMake 2.8 in its version
5 tree. This script adds the key and .repo file.

Prefix this with is_on_rhel5 predicate. Must run as root!
Merge pull request #3 from rolk/003_puias

Add PUIAS (aka. Springdale) repo (for CMake 2.8)