Comment # 78 on bug 939456 from H. Zeng

I tried again with the official ISO directly `dd`ed to the USB drive. This time
it has no problem to boot into installer.

Sorry for the false alarm. Either I had made a mistake or the ISO I downloaded
had certain glitch with it. The former ISO is the one I downloaded from
"15.0-Current" while the second one downloaded from "15.0". Their "last
modified time"s are different but I assume they are almost the same, right?

Anyway, there is no problem for T420s.

I am truly sorry for the extra work I caused, especially for Steffen.