I suspect the error that is output elsewhere is more revealing - can we use it instead (and for extra credit, merge them to use the same code?)

```
$ docker pull asdf/asdf/aa
2014/03/20 10:33:45 Invalid repository name (asdf/aa), only [a-z0-9-_.] are allowed
$ docker pull asdf///asdfaa                                                         
2014/03/20 10:36:05 Invalid repository name (//asdfaa), only [a-z0-9-_.] are allowed
```