More verbose errors for pickneglogsoftmax
More verbose errors for pickneglogsoftmax


Former-commit-id: 5fef6a003e673cf1bc6c69c0fb72f5916f646550
shuheik/dynet,xunzhang/dynet,clab/dynet,chunyang-wen/dynet,danielhers/dynet,xunzhang/dynet,chunyang-wen/dynet,shuheik/dynet,danielhers/dynet,danielhers/dynet,clab/cnn,clab/dynet,xunzhang/dynet,danielhers/dynet,clab/cnn,clab/dynet,clab/dynet,shuheik/dynet,danielhers/dynet,chunyang-wen/dynet,danielhers/dynet,xunzhang/dynet,shuheik/dynet,shuheik/dynet,clab/dynet,shuheik/dynet,clab/dynet,chunyang-wen/dynet,clab/dynet,shuheik/dynet,clab/cnn,danielhers/dynet