Permit packages with no files to omit %files entirely

Permit packages with no files to omit %files entirely
- Fixes the long standing obscure behavior of missing %files
  section causes build to complete without errors but without producing
  any packages either. Packages without files in them are perfectly
  valid (eg metapackages), requiring empty %files section for those
  is just unnecessary spec noise.
- Remove %files section on one of the test-suite specs to create
  a test-case for this as a side-effect.
- This of course introduces a slight incompatibility with older rpm's,
  if compatibility is required then just add those empty %files in the
  spec, they dont hurt anything but the readers eyes.