Do not include <quotearg.h>; no longer needed.

Do not include <quotearg.h>; no longer needed.
(boundary): New type.
(location_t): Use it.  This allows locations to span file boundaries.
All member uses changed: file -> start.file or end.file (as needed),
first_line -> start.line, first_column -> start.column,
last_line -> end.line, last_column -> end.column.
(equal_boundaries): New function.
(LOCATION_RESET, LOCATION_STEP): Remove.
(LOCATION_PRINT): Remove.  All callers changed to use location_print.
(empty_location): Now const.
(location_print): New decl.