adds support for building the model of a program for which the classpath is incomplete

I agree. See
https://github.com/INRIA/spoon/pull/57/files#diff-02487d213cf6039421911ce80f9d8cd3R304
and
https://github.com/INRIA/spoon/pull/57/files#diff-aa3bc70c72e14d26c8a0af1f70f6dc58R526