SpecFile is based after django.core.files.base.ContentFile, which lacks a __unicode__
method. This leads to an AttributeError when SpecFile.__repr__ is called. This is
easily resolved by giving SpecFile a proper __unicode__ method.
This extra layer of indirection allows us to tack some attributes
(name and content_type) onto the underlying file, which we cannot
do with a StringIO since it's a native ctype.
These attributes are used by various third-party software that expects
to work with django.core.files.File instances, and not directly with
StringIO instances. By way of example, the django-storages mosso
backend (CloudFilesStorage) looks for a content_type attribute, and
the cloudfiles Object backend looks for a name attribute.
