Total rewrite of the append function in order to have more control over the error conditions signaled in case of dotted lists.  Also added more comments to make the style more like "literate programming".
Total rewrite of the append function in order to have more control
over the error conditions signaled in case of dotted lists.  Also
added more comments to make the style more like "literate
programming".

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