import completion is unaware of pep 420 namespace packages.

When attempting to import a pep 420 namespace package, tab completion is not presenting the namespace packages.

Interestingly, after the namespace package is included in the line tab completion resumes working.

```
In [1]: import parent\t
```

Nothing...

```
In [2]: import parent_ns.pkg_\t
pkg_c
pkg_d
```
Here we got pkg_c and pkg_d options.