(scan_lists): When searching back for comment:

(scan_lists): When searching back for comment:
if comment-end is 2 chars, assume it does end a comment.
Otherwise, scan back to previous comment-end to see if there's
a comment starter between.  Also record whether the string quotes
between the start and the end are paired and uniform.
If so, skip to comment starter.  If not, scan from start of
defun to find comment starter if any.
(find_defun_start): New function.