Static view asset spec

Fixes the following scenario:

```ini
webassets.base_dir = 'package:static'
webassets.static_view = True
```

```python
request.static_url('package:static/foo.png')
```
True! Thanks. Will fix in a moment.
On Jul 10, 2014 10:19 PM, "Keith Yang" <notifications@github.com> wrote:

> In pyramid_webassets/__init__.py:
>
> >
> > -        return url
> > +        try:
> > +            return request.static_url(item)
> > +        except:
>
> It's always better practice to except SomeError or so then developers can
> know why it's passed.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/sontek/pyramid_webassets/pull/50/files#r14807222>.
>