Makefile: add more git support

Makefile

@@ -1,11 +1,24 @@
-all: update
+all: update_submodules
 	make -C js/rdf all
 	make -C js/mashup all
 
-.PHONY: all update
+update: pull
 
-update:
-	git submodule update --init
+update_submodules:
+	@@if [ -d .git ]; then \
+		if git submodule status | grep -q -E '^-'; then \
+			git submodule update --init --recursive; \
+		else \
+			git submodule update --init --recursive --merge; \
+		fi; \
+	fi;
+
+pull_submodules:
+	@@git submodule foreach "git pull \$$(git config remote.origin.url)"
+	@@git submodule summary
+
+pull: pull_submodules
+	@@git pull ${REMOTE} ${BRANCH}
 
 gh-pages: all
 	git branch -D gh-pages ||:
@@ -28,3 +41,5 @@ status:
 writable:
 	@sed -i -re 's/git:\/\/github.com\//git@github.com:/' .git/config
 	@make -sC js/rdf writable
+
+.PHONY: all clean update update_submodules pull_submodules pull