contiki/Makefile: Add in Contiki version check

Set to release/v4.9

examples/contiki/Makefile

@@ -1,12 +1,30 @@
 CONTIKI=contiki-ng
 TARGET?=native
 
-all: server
+WITH_CONTIKI_NG_BRANCH=release/v4.9
+
+all: $(CONTIKI) check-version server
 
 $(CONTIKI):
 	git clone --depth 1 https://github.com/contiki-ng/contiki-ng.git $@
+	echo "Updating $(CONTIKI) to ${WITH_CONTIKI_NG_BRANCH}"
+	(cd ${CONTIKI} ; git pull --tags 2> /dev/null ; git checkout ${WITH_CONTIKI_NG_BRANCH})
 	cd $(CONTIKI)/os/net/app-layer && rm -rf libcoap && ln -s ../../../../../.. libcoap
 
+check-version:
+	@(if [ -d $(CONTIKI) ] ; then \
+		cd $(CONTIKI) ; \
+		TAG=`git describe --tags --all`; \
+		if [ "$$TAG" != ${WITH_CONTIKI_NG_BRANCH} ] ; then \
+			if [ "$$TAG" != "tags/${WITH_CONTIKI_NG_BRANCH}" ] ; then \
+				git pull --tags 2> /dev/null ; \
+				echo "Updating $(CONTIKI) to ${WITH_CONTIKI_NG_BRANCH}" ; \
+				git checkout ${WITH_CONTIKI_NG_BRANCH} ; \
+				cd os/net/app-layer && rm -rf libcoap && ln -s ../../../../../.. libcoap ; \
+			fi ; \
+		fi ; \
+	fi)
+
 server:	$(CONTIKI)
 	$(MAKE) -f Makefile.contiki CONTIKI=$(CONTIKI) TARGET=$(TARGET) server