Raise error for account used only on the accessor

Because of the batch mode of Function field, the getter must not raise error
otherwise the error can be raised for a record that doesn't require the
account.
So we introduce an new kind of Function field which raise the error only at the
accessor level.

issue4087
review9531002

--HG--
extra : amend_source : e33fbb5321cdd2d8bfa7646014578624c0302c88