Fix setrefs.c comment properly.
The "typo" alleged in commit
1e460d4bd was actually a comment that was
correct when written, but I missed updating it in commit
b5282aa89.
Use a slightly less specific (and hopefully more future-proof) description
of what is collected. Back-patch to 9.2 where that commit appeared, and
revert the comment to its then-entirely-correct state before that.