Made S3BotoStorage deconstructible so that Django can migrate it.

[ramprabhuj]

Without this, Django 1.7 migrations fail with
ValueError: Cannot serialize: <storages.backends.s3boto.S3BotoStorage object at 0x1050a1358> There are some values Django cannot serialize into migration files.

[jschneier]

Hi and thanks for the pull request. Could you explain the use case for this a bit? As you can see S3BotoStorageFile is already deconstructible and the way of using it that I am familiar with in models is to use that as your field. How do you use the S3BotoStorage object in your models file?

[ramprabhuj]

You can specify
s3 = S3BotoStorage(params,...) image = models.ImageField(storage=s3,...)
Basically the Django FileField has a storage parameter and the user can pass any object that extends Storage

Without this PR the above code will fail in migration.

[jschneier]

Ah interesting, wasn't familiar with that use case, thanks for the explanation.