alignment_frame found the column by the left edge most of the page's other
rows share. On a page of two columns, a title over the column with fewer rows
took the other column's edge, failed to fit in it, and was aligned in its own
box. Only rows reaching across the title now count.
Tests: the two-column case; a two-colour title (the styled-region path) is
framed too; a justified paragraph sent with its rows split by line breaks, as
the editor sends it, still fills every row but the last.
RiceDee
ea6420cde5