DataFrame(d::Dict) trying to access d(:key).

here's the PR associated to the issue #625 

cheers
Let's move this up earlier, so that you have

```
columns = Array(Any, p)
colnames = Array(Symbol, p)

for j in 1:p
    ...
    colnames[j] = symbol(dnames[j])
end
```

That saves us one traversal of the array.