Make a shallow symlink farm

Make a shallow symlink farm

Fighting Cargo to avoid this has become too much hard work.

In particular, otherwise with workspaces we would have to edit all of
the member paths.  And having done that the sources themselves claim
to be part of a different workspace, so it's all awful.

I have also seen some weird behaviours where cargo didn't work quite
right because the package wasn't convincing enough.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>