minirst: improved support for option lists. This enables minirst to parse and print option lists which have both long and short options. Before, we could only parse option lists with long options.

test-subrepo-git.t: portability fix. Specifying arguments after file names for 'ls' is a GNU extension.

minirst: modified minirst to also recognize empty comments. The modifies minirst to also handle empty comments. An empty comment is a block with a single line containing two dots.

merge with stable