doc,maint: fix use of "i.e." in documentation and comments

doc,maint: fix use of "i.e." in documentation and comments

To align with all other places (and correct grammar), change all
upper-case "I.E." to "I.e.".  Furthermore, ensure that "i.e." is
followed by a comma.  Finally, ensure to use a double-space before
"I.e.," at the beginning of a sentence.

The following was used to change all offending uses (apart from
old ChangeLog files):

  $ git grep -liF 'i.e.' \
      | xargs sed -i \
            -e 's/I\.E\./I.e./g' \
            -e 's/\. \(I\.e\.\)/.  \1/g' \
            -e 's/\([Ii]\.e\.\)\( \)/\1,\2/g' \
            -e 's/\([Ii]\.e\.\)$/\1,/g'

* cfg.mk (sc_prohibit_uppercase_id_est): Add new rule.
(sc_ensure_double_space_after_dot_before_id_est): Likewise.
(sc_ensure_comma_after_id_est): Likewise.
(old_NEWS_hash): Refresh hash via "make update-NEWS-hash".
* NEWS: Change use of "id est" abbreviation via the above command.
* README: Likewise.
* README-prereq: Likewise.
* doc/coreutils.texi: Likewise.
* gl/lib/rand-isaac.c: Likewise.
* gl/lib/tempname.c.diff: Likewise.
* man/stdbuf.x: Likewise.
* src/cat.c: Likewise.
* src/copy.c: Likewise.
* src/copy.h: Likewise.
* src/cp.c: Likewise.
* src/cut.c: Likewise.
* src/dd.c: Likewise.
* src/df.c: Likewise.
* src/fiemap.h: Likewise.
* src/longlong.h: Likewise.
* src/ls.c: Likewise.
* src/numfmt.c: Likewise.
* src/pr.c: Likewise.
* src/shred.c: Likewise.
* src/shuf.c: Likewise.
* src/split.c: Likewise.
* tests/Coreutils.pm: Likewise.
* tests/df/df-symlink.sh: Likewise.
* tests/df/skip-rootfs.sh: Likewise.
* tests/init.sh: Likewise.
* tests/ls/color-norm.sh: Likewise.
* tests/misc/basename.pl: Likewise.
* tests/misc/ls-misc.pl: Likewise.
* tests/misc/md5sum-bsd.sh: Likewise.
* tests/misc/shred-exact.sh: Likewise.
* tests/misc/sort.pl: Likewise.
* tests/misc/stdbuf.sh: Likewise.
* tests/misc/tac-continue.sh: Likewise.
* tests/rm/r-root.sh: Likewise.
* tests/tail-2/symlink.sh: Likewise.