send-email: use the three-arg form of open in recipients_cmd

Perlcritic does not want to see the trailing pipe in the two-args form of open(), i.e. open my $fh, "$cmd \Q$file\E |"; If $cmd were a single-token command name, it would make a lot more sense to use four-or-more-args form "open FILEHANDLE,MODE,CMD,ARGS" to avoid shell from expanding metacharacters in $file, but we do expect multi-word string in $to_cmd and $cc_cmd to be expanded by the shell, so we cannot rewrite it to open my $fh, "-|", $cmd, $file; for extra safety. At least, by using this in the three-arg form: open my $fh, "-|", "$cmd \Q$file\E"; we can silence Perlcritic, even though we do not gain much safety by doing so. Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>