Add check-full to run testsuite of submodules

This model should be improved to avoid double-checking when the same
submodule could be installed or referenced by multiple levels...

Makefile

@@ -7,5 +7,14 @@ clean:
 config/environments/test.js: config/environments/test.js.example
 	./configure
 
-check: config/environments/test.js
+check-local: config/environments/test.js
 	./run_tests.sh
+
+check-submodules:
+	for sub in windshaft grainstore mapnik; do \
+		test -e node_modules/$${sub} && make -C node_modules/$${sub} check; \
+	done
+
+check-full: check-local check-submodules
+
+check: check-local