Modified the mapcar function to signal an error when one of the lists is not a proper list, rather than relying on cdr to catch it.
Modified the mapcar function to signal an error when one of the lists
is not a proper list, rather than relying on cdr to catch it.

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