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".