gfor example matmul failed

The code in example for gfor http://arrayfire.org/docs/page_gfor.htm (most bottom) fails.
```
// BEFORE
gfor (seq k, 400) {
  array B = A(span,k);
  C(span,span,k) = matmulNT(B * B);  // outer product expansion runs out of memory
}
```
Error message: matmul can not be used in batch mode