tap2rpm should allow setting RPM dependency information

[TimAllen]

I have a system that deploys a Python server to production, packaged in RPMs. Currently I have a distutils-based RPM that packages the server code, and a tap2rpm-based RPM that installs the startup script. Strictly speaking, the tap2rpm RPM depends upon the distutils RPM, but tap2rpm provides no way to record that dependency in the packages it produces.

tap2rpm should have command-line options to set the "Requires", "Provides" and "Obsoletes" in the RPMs it creates, so that they can be reliably deployed with yum or apt or other dependency-management tools.

[TimAllen]

This ticket split off from #3292.