we want to have a UCL file for every package, to set fields like
comment, desc, license, etc.; to avoid cluttering release/packages with
~200 new files, move these to the ucl/ directory.
add a better description for the yp package to demonstrate how this will
work in practice.
eventually, we should require the ucl file exists (try=false) to prevent
people accidentally creating new packages with a typo, but for now, keep
the ucl optional.