whonix_shared/usr/lib/whonix/whonixcheck/50_check-whonix-news: fix (because there is now a /usr/share/whonix/keys/whonix-keys.d/placeholder file), fix error message when verification fails, refactoring, comment
fix
"which" -> "command -v" as per http://mywiki.wooledge.org/BashFAQ/081