Code review comment for lp:~rye/ubuntuone-client/stop-killing-thumbnails

> Could you please describe what this branch does?

This branch fixes #491777 by creating internal hash for all file objects that were handled to us by Nautilus in ubuntuone_nautilus_update_file_info. Later on this info is used to request nautilus to invalidate extension date (in our case - emblems). After the call tonautilus_file_info_invalidate_extension_info the emblems get cleared and a call of ubuntuone_nautilus_update_file_info is performed.
The old method, updating the modification time for a file caused the thumbnails to be regenerated and is a pretty nasty practice, since other applications might use these timestamps for their purposes.