When the validation state is already 'validated', upon edition, set the new
value to 'text_content_non_validated' property instead of 'text_content' for
the following reasons:

 1/ It allows to validate the source code through Component validation
    workflow rather than after each edition;

 2/ It avoids dirty hacks to call checkConsistency upon edit and deal with
    error messages, instead use workflow as it makes more sense.

Then, when the user revalidates the Component through a workflow action,
'text_content_non_validated' property is copied back to 'text_content'.