New Migration procedure

[Rainer Müller]

Hey,

as registry 2.0 with 'portdbformat sqlite' stores the platform a port
was built and installed on, the migration procedure [1] needs to be
rewritten for the upcoming Lion release.

'port outdated' will consider all installed ports as outdated with a
note saying "(platform darwin 10 != darwin 11)".

It's no longer necessary to manually remove and reinstall all ports or
use a script for that, instead this can be solved by running the command
'port upgrade outdated'. Of course the migration will only be that easy
if no build failures occur.

Rainer

[1] http://trac.macports.org/wiki/Migration