Convert .rpm files for extraction with /usr/bin/cpio

Quoting the author:

why does the world need another rpm2cpio?  because the existing one
won't build unless you have half a ton of things that aren't really
required for it, since it uses the same library used to extract RPM's.
in particular, it won't build on the HPsUX box i'm on.

(this one needs just perl)