doc: clarify in --help that -Z doesn't take an argument

* NEWS: Fix a confusing old entry.
* cfg.mk (old_NEWS_hash): Adjust accordingly.
* src/cp.c (usage): Separate the -Z and --context descriptions.
* src/install.c: Likewise.
* src/mkdir.c: Likewise.
* src/mkfifo.c: Likewise.
* src/mknod.c: Likewise.
Fixes http://bugs.gnu.org/17220
maint: document timeout --preserve-status in v8.21 NEWS

* NEWS: Add the omitted new feature.
* cfk.mk (old_NEWS_hash): Adjust accordingly.
maint: avoid static analysis warnings in ln.c

* src/ln.c (do_link): It's not obvious that record_file() is a noop
in the symlink case (in that case dest_set is NULL and so ignored).
So to make it obvious, and to avoid false positives seen in coverity,
add the explicit condition here.
tests: fix false dd conv=sparse failure on newer XFS

* tests/dd/sparse.sh: When testing that a hole is created,
use an existing sparse destination file, so that we're
not write extending the file size, and thus avoiding
speculative preallocation which can result in smaller
holes than requested.
Workaround suggested by Brian Foster
maint: df: avoid sizeof(char**) static analysis warning

* src/df.c (alloc_table_row): Use the size of char** to enlarge
the table.  Spotted by Coverity.
doc: improve remove prompt translator comment

* src/remove.c (prompt): Explain where the difficulty with translating
these two strings resides, and suggest an alternative: the one that
Paul Eggert first proposed back in 2002, which seems fully resistant.
ls: don't output colors with unknown TERM env variable

--colors controls whether to output colors depending on
whether we're connected to a terminal or not, while this
change gives control over which terminals we output colors to.

* NEWS: Mention the change in behavior.
* src/ls.c (known_term_type): A new function to search the static
list from dircolors.h
(parse_ls_colors): Honor the TERM when both LS_COLORS and COLORTERM
are non empty.
* tests/ls/color-term.sh: A new test.
* tests/local.mk: Reference the new test.
Fixes http://bugs.gnu.org/15992
dircolors: add hurd and mach-gnu-color terminal types

mach-color was replaced by mach-gnu-color in Hurd in 2012.
mach-color is left for compatibility and corresponding
definitions for mach-color are still found in ncurses.

* src/dircolors.hin: Add hurd and mach-gnu-color.
doc: disambiguate chmod man page reference to (a) users

* man/chmod.x: Don't rely on the bold markup for 'a' to
distinguish it as that's not done in all cases.