[FIX] base: compare on original module

Introduced at 574f4c3d
model._module has for value of the last module extending the model.
This means that, when a module B inherit from a model defined in a module A (e.g
to add a field on the model), an external id, tagged with module B, will be
created for each field of the model, including the one defined only in A.

The intention of the patch at 574f4c3d was to include the automatic fields (i.e.
LOG_ACCESS_COLUMNS) into the condition.
Without that condition, the fields such as create_date were deleted when
upgrading a module (not defined in any module)