[storages] fix fs_importing side-effect on entity.data
When creating a new File object, if fs_importing is set,
we want entity.data to be the file content instead of the
filepath for the rest of the transaction.
(see test_bfss_fs_importing_transparency) for test implementation
To make this possible, the storage hooks (entity_added / entity_updated)
must return the correct value to set in the entity dict.
About this site===============This web application is based on the CubicWeb knowledge management systemfrom Logilab_. CubicWeb is made of an object database and a webframework. It allows to develop an application by defining a set ofentities and their relationships, plus a set of views that present thedata selected from the object database using a specific query language.This application has a precise schema_ and can be considered anexample of a semantic web database, as it can export the data to XMLand others formats and is not limited to publishing HTML.Supported formats: |microformats|_ - JSON_ - |rss|_ - |dublincore|_..|microformats|image:: /data/microformats-button.png.._microformats: http://microformats.org.._JSON: http://www.json.org/..|rss|image:: /data/rss-button.png.._rss: http://www.rssboard.org..|dublincore|image:: /data/dublincore-button.png.._dublincore: http://dublincore.org.._Logilab: http://www.logilab.fr/.._schema: schema