Currently we pass only the columns based on the screen-width, which is
important for the carets. But we don't pass the bytes-based columns,
which is important for the colors. Pass both.
* src/muscle-tab.c (muscle_boundary_grow): Also pass the byte-based column.
* src/location.c (location_caret): Clarify.
(boundary_set_from_string): Adjust to the new format.
* tests/diagnostics.at (Tabulations and multibyte characters from M4): New.
386cf25088