Build Enviroment
M4
Sometimes, packages need a version of m4 that is not in the standard release in order to build. The version that SL5 has used is here.
http://ftp.scientificlinux.org/linux/scientific/5x/SRPMS/SL/m4-1.4.8-1.src.rpm
This version is not in the release, because it would then make the release incompatable with The Upstream Vendor.