Redirect stderr of scp(1) to stdout to not indicate errors

Redirect stderr of scp(1) to stdout to not indicate errors

Some warning messages of scp(1) are written to stderr (like "Connection
to ... closed by remote host."), even when there is no error and the
exit code is 0 ("no error"). Therefore redirect stderr to stdout to not
confuse "mail wrapper scripts" that see output on stderr otherwise.