replacing a member, and 'a' when adding one.
* ar.c (truncate): New static variable.
(normalize): Change return type to const char *. Add abfd
argument. Change all callers. If truncate, chop the filename to
abfd->ar_max_namelen.
(main): For the 'f' modifier, set truncate to true. Don't change
quick_append to replace to truncate is true.
(do_quick_append): If truncate, set BFD_TRADITIONAL_FORMAT.
(write_archive): Likewise.
* binutils.texi, ar.1: Document 'f' modifier.
PR 6888.
