LazyObject fools get_thumbnailer

[funkybob]

DefaultStorage derives from LazyObject, and so does not test true as an instance of Storage

>>> from django.core.files.storage import default_storage, Storage
>>> isinstance( default_storage, Storage )
False
>>> default_storage
<django.core.files.storage.DefaultStorage object at 0x2ac735da22d0>

[funkybob]

A quick workaround is to change line 45 of files.py from:
source = default_storage
to:
source = get_storage_class()()

Tested and workig [though possibly not ideal.]

[SmileyChris]

Fixed in f6890af