jedi:complete: force completion after stop words

Here's a minimalistic test that fails for me:

```python
import unittest

unittest.as
```

With point after "as" activating `jedi:complete` does nothing, unlike `auto-complete` which initiates completion successfully. Apparently "as" is considered a stop-word after which completion is usually unwanted (unless requested specifically by a command) and `jedi:complete` doesn't convey the fact that auto-completion is triggered by a command.

I'm by no means an expert in `auto-complete` internals, but the patch works for me.