Total rewrite of the list-length function to have better control over error signaling in case of dotted lists.  Also added more comments in order to make the style more like "literate programming".
Total rewrite of the list-length function to have better control over
error signaling in case of dotted lists.  Also added more comments in
order to make the style more like "literate programming".

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