validate_address can't handle display name

This looks like a possible bug; address.validate_address returns none when passed a email string with a display name. Yet parse can handle it.

```python
>>> text = 'Fooman '
>>> address.validate_address(text)
>>> None
>>> address.validate_address('fooman@bar.com')
>>> fooman@bar.com
```

```python
>>> address.parse('Fooman ')
>>>Fooman
```

Start at the address.validate_address entry point and compare its handling of the display-name input with address.parse, using the examples in the issue to reproduce the behavior. Done means validate_address accepts the display-name form consistently with the plain email form and no longer returns None for that input.

Written by the indexing model from the issue text.