SINGA-474 mul operator, modified backward test
SINGA-474 mul operator, modified backward test

nudles/incubator-singa,nudles/incubator-singa,nudles/incubator-singa,apache/incubator-singa,nudles/incubator-singa,apache/incubator-singa,apache/incubator-singa,nudles/incubator-singa,apache/incubator-singa,apache/incubator-singa