coreutils: keep lines within 80-column limits

coreutils: keep lines within 80-column limits

* cfg.mk (LINE_LEN_MAX, FILTER_LONG_LINES): New macros.
(sc_long_lines): New rule.
* HACKING: Use shorter URLs to the same material.
* doc/Makefile.am, doc/coreutils.texi, m4/boottime.m4:
* man/help2man, man/stdbuf.x, src/Makefile.am, src/cat.c, src/copy.c:
* src/cp.c, src/dd.c, src/df.c, src/du.c, src/groups.c, src/install.c:
* src/ls.c, src/md5sum.c, src/mv.c, src/od.c, src/pinky.c, src/ptx.c:
* src/readlink.c, src/remove.c, src/rmdir.c, src/setuidgid.c:
* src/sort.c, src/tail.c, src/touch.c, tests/Coreutils.pm:
* tests/cp/existing-perm-race, tests/cp/perm, tests/cp/preserve-gid:
* tests/du/2g, tests/du/long-from-unreadable, tests/init.sh:
* tests/install/basic-1, tests/ls/nameless-uid:
* tests/ls/readdir-mountpoint-inode, tests/misc/chroot-credentials:
* tests/misc/cut, tests/misc/date, tests/misc/join, tests/misc/md5sum:
* tests/misc/sha1sum, tests/misc/sha224sum, tests/misc/sort:
* tests/misc/sort-continue, tests/misc/sort-files0-from:
* tests/misc/sort-rand, tests/misc/stdbuf, tests/misc/tr:
* tests/misc/uniq, tests/mv/atomic, tests/mv/part-fail:
* tests/mv/part-symlink, tests/mv/sticky-to-xpart, tests/pr/pr-tests:
* tests/rm/fail-2eperm, tests/rm/interactive-always:
Reformat to fit within 80 columns.
* doc/Makefile.am (BAD_POSIX_PERL): New macro.
* doc/coreutils.texi: Reword slightly, to make menus and
index lines shorter.
* src/md5sum.c: Redo --help output so that it fits within 79
columns, since that's a bit more portable and all the other --help
strings fit in 79 columns.