Added test for FROM - TO - BY with NIL as a variable.
Added test for FROM - TO - BY with NIL as a variable.

clasp-developers/SICL,clasp-developers/SICL,vtomole/SICL,vtomole/SICL,clasp-developers/SICL,clasp-developers/SICL,vtomole/SICL,vtomole/SICL