colspanned columns should inherit tag

[takuy]

Colspanned columns need to inherit the tag of the original column. Otherwise, in a header row, this leaves you with a bunch of th tags separated by tds tags (since the default is to treat an empty tag as td per https://github.com/cosmocode/edittable/blob/09298eaff7a6ebcb9892511587fac055380c5653/action/editor.php#L222)

When the array is parsed by build_table, this means the table is actually malformed per DokuWiki syntax and what should be a ^ ends up being a |; this later generates bad or unexpected HTML - th elements end up in tbody instead of thead.