Tidyup, and make all the commands that take a package identifier
behave the same.  Previously, naming a package without a version
number only matched the same package identifier, if you wanted to
match multiple packages you had to say P-*.  However, the new list and
latest commands behave differently, which was inconsistent.

I believe the previous behaviour was for backwards compatibility with
packages that had no version number.  However, it's unlikely that this
is ever useful, so I've changed the semantics so that a package name
on its own matches all versions of that package.