RFR 8165405: jshell tool: /classpath is inconsistent

[Robert Field]

Please review....

Bugs:

    jshell tool: /classpath is inconsistent
    https://bugs.openjdk.java.net/browse/JDK-8165405

    JShell: crash in TaskFactory$WrapSourceHandler.diag
    https://bugs.openjdk.java.net/browse/JDK-8172103

Webrev:

    http://cr.openjdk.java.net/~rfield/8165405v1.webrev/

Thanks,
Robert