This improves on the original fix to #5285 by preventing
other mixed lists (lists with a mix of Plain and Para
elements) that were allowed given the original fix.
This is now the default for pandoc's Markdown.
It allows whitespace between the two parts of a
reference link: e.g.
[a] [b]
[b]: url
This is now forbidden by default.
Closes#2602.
The org writer was inserting two spaces after list bullets. Emacs
Org-mode defaults to a single space, so behavior is changed to reflect
this.
Closes: #3417
