Erroneous check for partial block in tutorials/vector_addition.cu

```
I believe line 80 should read:
  if(num_elements % block_size) ++grid_size;

instead of the current:
  if(grid_size % block_size) ++grid_size;

In other words, add an extra block to the grid if the total number of
elements isn't evenly divided by the block size.
```

Original issue reported on code.google.com by `mark.jar...@gmail.com` on 7 May 2010 at 7:26
