created "tests" subdirectory infrastructure

tests/Makefile

@@ -0,0 +1,14 @@
+
+all:
+	for d in *; do \
+		if [ -d $$d ]; then \
+			make -C $$d; \
+		fi; \
+	done
+
+clean:
+	for d in *; do \
+		if [ -d $$d ]; then \
+			make -C $$d clean; \
+		fi; \
+	done