Locations issued from M4 need the byte-based column for the
diagnostics to work properly. Currently they were unassigned, which
typically resulted in partially non-colored diagnostics.
* src/location.c (boundary_set_from_string): Fix the parsed location.
* src/muscle-tab.c (muscle_percent_define_default): Set the byte values.
* tests/diagnostics.at (Locations from M4): New.