Allow DjangoObjectPermissions to use views that define get_queryset

[ticosax]

New version of #2864

The noticeable change compare to #2864 is that we do not catch anymore AttributeError

try:
    queryset = view.get_queryset()
except AttributeError:
    # the Attribute error will not catch what we want
    # because hasattr(view, 'get_queryset') will always return True
    # the only AttributeError we will catch is comming from the .get_queryset()
    # method itself during execution, which is really bad.
    queryset = getattr(view, 'queryset', None)
except AssertionError:
    # view.get_queryset() didn't find .queryset
     queryset = None

[tomchristie]

Should we just be using exactly the same style as here?... https://github.com/tomchristie/django-rest-framework/pull/2863/files#diff-d5f4b02a7b88b58fe3990de607a06d8fR110

[ticosax]

APIRoot view doesn't have get_queryset() method.

[ticosax]

@tomchristie Sorry I didn't saw your comments.
I closed it because I realized my assumption was wrong, not all views has .get_queryset() defined.
I will write a test with APIRoot support and take into account your comments.
thank you for your patience.