jmod problem

[Jonathan Gibbons]

I have a reasonably up to date copy of the jigsaw forest, and I have 
built it successfully on Ubuntu.

If I try and run jmod to create a simple library, it tells me it cannot 
find the parent library, and indeed, the path it specifies does not exist.

>  % ./build/linux-amd64/j2sdk-image/bin/jmod create -L /tmp/xxx
> /tmp/xxx: Cannot open parent library 
> /mnt/w/jjg/work/jigsaw/jigsaw/build/linux-amd64/j2sdk-image/jre/lib/modules

Am I out of date with how things are supposed to work?   Is jmod in 
j2sdk-image supposed to work?

This is breaking one of the langtools regression tests.

-- Jon