If PATH environment variable is not defined, this Products cannot be
imported. Followup of 399f95f9.

There are a lot of misses in this function because related keys must have
precedence over homonym columns, which makes it cost a *lot* of cpu time
to just return None.

Not perfect yet (what if definitions change during the same transaction ?),
but better than previous state.

it was creating local properties

With this, is possible set custom references without overwrite accounting_workflow

- The interface says that getConversionSize raises a KeyError when this cache
  does not exist. Update implementation accordingly.
- update getConversion to always return a string for the data. The caller
  should not have to worry about the data format.
- warn when an OFS.Image is passed to setConversion

Updating local roles may depend on many things, like categories, and developers
should not be forced to put all dependencies in a separate BT that would be
installed before.

now it is filename, not file_name.

Fix dependency of erp5_simulation_test now that erp5_trade does not depend on erp5_simulation anymore

See also commit af640e28

otherwise Web Section or Web Site without default Web Page does not contain cache related headers.

so that pages rendered as authenticated will never be displayed after logout.