[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.

"""pre 3.6 bw compat"""
# pylint: disable-msg=W0614,W0401
from warnings import warn
warn('moved to cubicweb.uilib', DeprecationWarning, stacklevel=2)
from cubicweb.uilib import *