Plone-app-blob

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- ATImage adapter should take care of cases where no image was uploaded.
[gotcha]

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- Test fixes.
[davisagli]

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- Avoid breaking on startup if PIL is not present.
[davisagli]

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- Adjust tests to the fixed spelling of 'kB'.
[witsch]

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- Fix the ``type`` of blob-based fields so they are distinguishable as
blob fields.
[davisagli]

- Fix broken migration-forms.
[WouterVH]

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- Properly close written blobs in all `IBlobbable` adapters in order to
avoid `POSKeyErrors`.
This fixes http://plone.org/products/plone.app.blob/issues/43
[jbaach, witsch]

- Allow explicitly setting a mimetype via a keyword passed to the mutator.
[davidblewett, kleist, witsch]

- Don't raise `AttributeError` when calling `getSize` on empty images.
[ggozad, witsch]