Build system does not respect DESTDIR by default.

--- a/Makefile.in
+++ b/Makefile.in
@@ -203,9 +203,9 @@
 # "make install" installs the programs in BINDIR
 #
 install:
-	mkdir -p ${BINDIR}
+	mkdir -p $(DESTDIR)${BINDIR}
 	for file in $(PROGS); do\
-		cp src/$$file $(BINDIR)/;\
+		cp src/$$file $(DESTDIR)$(BINDIR)/;\
 	done
 #	if test -d $(RIGFILTERS); then\
 #	   for file in $(RFPROGS); do\