RelEx2Logic: temporary work-around for post-processing

Temporary work-around for post-processing code, assuming any R2L link that only contains one instanced word does not need post-processing... which is wrong, because you can have

```
EvaluationLink
    not
    run@1234
```

which does need to be included in post-processing.  A new way is needed to classify the different type of R2L output.

Also not too sure what would an abstracted version of a VariableNode be like.

Note: now `create-abstract-version` requires InterpretationNode instead of ParseNode.

P.S.  Here's the original discussion about abstract representation in case anyone is interested:
https://docs.google.com/document/d/1RQmL084Qlel9ky2eNSvnPDd3MMuRhpbDlsMG_db4odQ/pub