[plt-scheme] schemeunit: require/expose stopped working in 370

I just upgraded mzscheme to 370 from 369.something, and one of my
tests, which uses require/expose, has stopped working.

Here's the code.  The first file is named "at-private.ss":

    #! /bin/sh
    #| Hey Emacs, this is -*-scheme-*- code!
    exec mzscheme -qr "$0" ${1+"$@"}
    |#

    (require
     (planet "util.ss"    ("schematics" "schemeunit.plt" 2)))
    (require/expose "auction.ss" (a-risk))

Now here's "auction.ss" (I'm not convinced that the content of this
file is relevant, but hey):

    #! /bin/sh
    #| Hey Emacs, this is -*-scheme-*- code!
    exec mzscheme -qu "$0" ${1+"$@"}
    |#

    (module auction mzscheme
      (define (a-risk a)
        1234))

Here's what I type, and what I see:

$ ./at-private.ss
    default-load-handler: cannot open input file: "/home/erich/.plt-scheme/planet/300/370/cache/schematics/schemeunit.plt/2/6/plt/auction.ss" (No such file or directory; errno=2)

The problem, of course, is that error message.  It didn't come up in
the previous version of mzscheme.  Obviously the file name in the
message is suspicious; the file "auction.ss" is in the current
directory (which happens to be /home/erich/doodles/bridge/auction.ss,
if it matters), not deep in the planet cache.

-- 
Keaton, Chaplin, Garbo - let them now make room for Gromit.
        A. O. Scott, in The New York Times