Change in semantics:
  - commands which only inspect the databse (list,describe,field)
    now take into account the user database unless --global is
    given.  This behaviour matches GHC, which also uses the user
    database by default.
  - However, commands which modify the database still use the
    global database, unless --user is given.

Also, allow P-* to be given as a package identifier, which means
"all versions of package P".