Mac ports migration: Cleanliness is next to—or in this case necessary for—functionality

Short version: If you installed/used mac ports (formerly darwin ports i think?) under Mac OS 10.8 say, and you're now running 10.10, follow the instructions in https://trac.macports.org/wiki/Migration and skip no steps. In particular don't skip sudo port clean all, though it may take a long time (over 45 minutes in my case).
(Some) details follow.

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A few years ago I installed some software on this macbook^® pro using the marvelous and wonderful mac ports system. Then, more recently, after interminable nags from Apple^®;’s Software Update™ program, I succumbed and updated "Snow Leopard" (?) to Mac^® OS X^® Yosemite™.

The fly appeared in the ointment when I tried to use the “old” ports with OS X Yosemite. I got a bunch of messages about how this and that were incompatible, and was urged to follow instructions at some web address, which redirected me to https://trac.macports.org/wiki/Migration; this has clear, detailed instructions on What Must Be Done. And so I followed them. Sort of.

I did something silly, though, which messed things up for a while. I got to the part that says “sudo port clean all” and after 5-10 minutes of seeing stuff scroll off the page, I said, "Hurmpf, I don't know we really need to do all that. I mean, I don't recall having any partly completed installs."

I can hear you now. "You idiot! What about the one that aborted and told you to do the migration??!" Exactly.

So I repeated the instructions. When I got to the "clean all" part, I ran that command under time(1) and went for a swim. I came back and found it still running! To add to my vexation, I had cats (Tiger Lily and Maka) fascinated by the smell of pool-water on my feet. The "sudo port clean all" took nearly 46 minutes. That's right, the better part of an hour.

I followed the rest of the instructions on the page and everything Just Worked. Good news.