Use ftp(1) instead of tools from the ports tree.

Index: cdiff.sh
--- cdiff.sh.orig
+++ cdiff.sh
@@ -30,7 +30,9 @@
         case `echo "$file" | perl -ne 'print lc $_'` in
         http:*|https:*|ftp:*)
             if [ -z "$CDIFF_FETCH" ]; then
-                if type curl >/dev/null 2>&1; then
+                if type ftp >/dev/null 2>&1; then
+                    CDIFF_FETCH="ftp -V -o -"
+                elif type curl >/dev/null 2>&1; then
                     CDIFF_FETCH="curl -s"
                 elif type wget >/dev/null 2>&1; then
                     CDIFF_FETCH="wget -e timestamping=off -qO -"
