Some good progress on permalinks and reindexing for Foal

[Daniel Gruno <hu...@apache.org>]

Hi folks,
I've been working on allowing old permalinks to work with 
migrated/reindexed emails, meaning once you migrate to Foal, you could 
use the new pibbles as your base ID, but still retain any old IDs you 
used in the old database.

As an example, consider the following thread:

https://lists.apache.org/x/thread.html/rcb64d3d87c22c5d17797e4f9dcf720db8894e5fa62dab5072c6af215@%3Cusers.httpd.apache.org%3E

This is currently available on the demo as:
https://foal-demo.ponymail.apache.org/thread/2povtzg6mmwjxs94

However, it is ALSO available using the same ID from lists.a.o;
https://foal-demo.ponymail.apache.org/thread/rcb64d3d87c22c5d17797e4f9dcf720db8894e5fa62dab5072c6af215@%3Cusers.httpd.apache.org%3E

AND it's, as always, available via Message-ID as well:

https://foal-demo.ponymail.apache.org/thread/%3CCAFMGiz-cJHQuELkU10AbRpGSwiraJHYzY298fJhmMqTVpkNuiA@mail.gmail.com%3E

Whenever someone grabs a permalink for it, it will always suggest 
2povtzg6mmwjxs94, but will honor any of the older methods.

I think this is good progress :)

With regards,
Daniel.

PS: The migration tool is not yet complete, so this is just an example 
of using two generators (cluster and dkim) on a 3rd party email that 
previously only had the cluster generator enabled.