maint: script diagnostics status cleanup

maint: script diagnostics status cleanup

Problem reported by Bruno Haible (Bug#29266#20).
* NEWS: Mention this.
* gunzip.in, gzexe.in, zcat.in, zcmp.in, zdiff.in, zforce.in:
* zgrep.in, zless.in, zmore.in, znew.in:
Use printf instead of echo if the argument might contain ‘\’, at
least in theory.  Don’t assume printf exits with status 1 on
failure; it might be some other positive status.
* gzexe.in: Use printf consistently instead of echo, and
proscribe it instead of echo.