* src/ltlparse/public.hh (fix_utf8_locations): New function.
* src/ltlparse/fmterror.cc (fix_utf8_locations): Implement it.
(format_parse_errors): Rename as ...
(format_parse_errors_aux): ... this.
(format_parse_errors): New implementation that call fix_utf8_locations()
before format_parse_errors_aux() on valid utf8 strings.
* src/ltlparse/Makefile.am: Include $(top_srcdir).
* src/ltltest/utf8.test: New file.
* src/ltltest/Makefile.am: Add it.
* src/ltltest/parse.test: Fix header.