Cfg spec

Just as a communication tool, I am creating a pull request for the work I had been doing on xsce.spec.in.  It interacts with the Makefile, in the same manner that the xs-config.spec did.  It's more complicated that the direct build spec. But permits the name of the built rpm to be changed by the makefile easily.  It seems like a valuable thing to me long term. But I'm not sure.

This pr works, and geneerates a set of RPMs, by issuing the command "make rpm". But this approach requires that a tag be placed on the build branch in order to work. We have not placed the v0.5 tag yet on master (which I think we should do).