Fix unzip-alist to actually work as the function name suggests

[hraban]

The original iterative version made little sense, especially using the on keyword instead of in. It did not work as intended.

To make this work on a more friendly sibling of the alist (namely, nested lists: ((a 1) (b 2) (c 3))), use #'first and #'second instead of #'car and #'cdr, respectively.

[zkat]

Nice catch, although s/on/in/ should be more than sufficient to fix this. I like that it collects both lists in a single iteration.

[adlai]

I incorporated your changes in 1bcac34 and bf6eec2, although the iterative algorithm stays.

[hraban]

Aye, thanks for that. "Caring about the implementation details of internal utility function unzip-alist in the chanl project" is relatively low on my TODO-list. As you can see, I am not a difficult man.