[MERGE] fields: cleanup field_to_dict + make @deprecated available in fields_get()

[MERGE] fields: cleanup field_to_dict + make @deprecated available in fields_get()

Renamed the m2m extra info keys, as their names
were quite confusing (third_table?), + removed
the "func_obj" key for function fields, as
it was a duplicate of the "relation" kay that
is already present for all relationship fields.
These renames should not break anything, as this
info should only be used for debug, but they still
constitute an API backwards-incompatible change.

bzr revid: odo@openerp.com-20120926162638-ftfbvflfa525q0lg