Improved exception info

If the NoReverseMatch exception occurs in the URLExtension._reverse method, there is an attempt of new reverse with the project name. But only the second exception has been raised if reverse fails again.
So, if I made a mistake in my urls.py:
```python
# some/urls.py
url(r'^some-incorrect-url-pattern$', view, name)
```
and included its with some namespace:
```python
url(r'^', include('some.urls', namespace='some-namespace'))
```
I have the wrong exception message <b>u'projectname.namespace' is not a registered namespace</b>.
It would be nice, if the initial exception will be raised.