where we want to take the disklabel filesystem type of "4.2BSD" and use
fsck_4.2bsd on those filesystems.
Add a comment about why the code is there, now that we know:
* XXX This is a kludge to make automatic filesystem type guessing
* from the disklabel work for "4.2BSD" filesystems. It does a
* very limited subset of transliteration to a normalised form of
* filesystem name, and we do not seem to enforce a filesystem
* name character set.