boolean indexing giving faulty results

Consider this:

```
a = af.constant(0., d0=3, d1=3)
a[1,1] = 1.
```

This one makes the whole second row into 2s:
`a[a>0.] = 2.`
While pavanky's trick gives the correct result:

```
cond = a>0
a = a*(1-cond)+cond*2.
```

Update: this also gives wrong results:
`a[af.algorithm.where(a>0.)] = 2.`
