HC-1025 restore image bytes

Copied from pre-subtree hydra:
https://github.com/bovardtiberi-wf/pdf_client_service/pull/30
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We do not want to erase image.bytes as there may be other references to this same image object in other parts of the pdf.

Test with the Box/pdf*/*Crow_demo_092512.pdf. Page 11 uses about five references of the small spreadsheet screenshot image: http://screencast.com/t/Io4eW697se52

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