Third try!

Makefile.in

@@ -24,8 +24,12 @@ clean:
 	cd Doc;$(MAKE) -j ${numCores} clean
 	mvn -T ${numCores} clean
 
-install:
+check-install:
+ifndef DESTDIR
+        $(error DESTDIR is undefined)
+endif
+
+install: check-install
 	rsync -av --exclude \*.jar --exclude \*VAADIN\* --exclude \*.class --exclude=__figurelink\* --delete P Doc/target/webhelp/ \
           freedocs@prog.mi.hdm-stuttgart.de:${DESTDIR}
-
 #end