Multiple parser and formatter fixes for line drawing in tbl(7).

Multiple parser and formatter fixes for line drawing in tbl(7).
* Allow mixing vertical line bars with the layout options
of the preceding layout cell.
* Correctly combine box options with layout lines.
* Correctly print vertical lines in data rows, with the right spacing.
* Correctly print cross markers and left and right ends of
horizontal lines even if vertical lines differ above and below.
* Avoid the bogus error message "no table data cells"
when a table data section starts with a horizontal line.
No increase in code size.