PROOFPATH or the like would be useful

[boyland]

Now that (unparameterized) modules are accepted, it would be helpful to be able to use multiple class paths, rather than a single one.

[boyland]

--path= has been added to the command-line and built-in library access has been added to both the command-line tool and to the Eclipse plugin. A larger "build-path" approach for the Eclipse plugin will await later changes.