I don't know why, but I can't seem to build the cog vm when I
RE-unpack OpenSourceCog.tar.gz.

The directory I unpacked it to earlier today still builds a VM just
fine.  I've renamed that one to .old for now, but I'm wanting to get
this VM into our standard build process and that involves unpacking
the tarball and building fresh via a script called by make.

But when I unpack OpenSourceCog.tar.gz and build it exacly the same,
it _appears_ that all builds fine, although it does seem perhaps a bit
longer.  When I then try to start an image, it says it can't find the
X11 plugin at:

  /my/specified/prefix/lib/squeak/3.9-7//vm-display-X11

Notice the double-slash; that's where it says it's looking for it,
which is obviously incorrect.

I had specified my prefix without a / suffix, which I assume is correct.

  make install prefix=/my/specified/prefix

I've been pulling my hair out because the one out of my cog.old
directory builds a perfectly-working VM using these exact same steps,
which I thought were merely unpacked from OpenSourceCog.tar.gz..

Any ideas?