I have now migrated the trac tickets to github issues.
I have been able to move all tickets (including closed ones), except the first ten (because I had already created 10 tickets in github, and I wanted to keep the numbering unchanged).
Unfortunately, the identities of submitters and commentators has not been kept during the migration, so that all tickets and all comments appear to have been created by me… This is annoying, because some conversations will be less clear, but I don't think it's a too big issue.
I have disconnected the old trac site, so please now use github for tickets. Don't forget to subscribe to notifications if you want to be kept informed.