Switch device database to cdb(5)

Hi all,
the attached patch removes another db(3) user from libc. The database
creation is much faster, the overall impact of creating both database
should be neglectable. As usual, the cdb version is ~1/4 of the size of
the db(3). I've dropped the complication of the caching code in
ttyname(3). Not having access to the database is the exception case and
I expect /dev to cached, if necessary, making it still fast enough.
There is one visible functional change. devname(3) will return pts/
entries for devices not open. I'm not sure if we have to / want to stat
in that case to verify the existance. Not doing it has the advantage of
working e.g. for ps(1).

Joerg