Use 'mv -f' in rc.d/ntpd to avoid spuriously halting the boot.

The final 'mv' to install a fetched leap-list file can fail (due to a
readonly fs, or schg flags, for example), and that leads to mv(1)
prompting the user, stopping the boot process.  Instead, use mv -f
to supress the prompting, and if verbose mode is on, emit a warning
that the existing file cannot be replaced.

PR:		219255

etc/rc.d/ntpd

@@ -148,7 +148,8 @@ ntpd_fetch_leapfile() {
 		     "$ntp_expiry_tmp" -eq "$ntp_expiry_db" -a \
 		     "$ntp_ver_no_tmp" -gt "$ntp_ver_no_db" ]; then
 			$verbose using $url as $ntp_db_leapfile
-			mv $ntp_tmp_leapfile $ntp_db_leapfile
+			mv -f $ntp_tmp_leapfile $ntp_db_leapfile ||
+			    $verbose "warning: cannot replace $ntp_db_leapfile (read-only fs?)"
 		else
 			$verbose using existing $ntp_db_leapfile
 		fi