Added test to check that append preserves the structure of the last list.
Added test to check that append preserves the structure of the
last list.

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