Caution when you update seeddms with workflow mode `advanced`
=============================================================

The previous database layout for tracking the workflow state of a
document content was not very well done. It did not allow to run
the document through another workflow at a later time, expecially
the same workflow, e.g. for a scheduled revision of a document.

Technical details
==================
This update modifies the tables tblWorkflowDocumentContent and
tblWorkflowLog. It adds a new autoincrement field as a primary key
(id) to tblWorkflowDocumentContent and references that field in
tblWorkflowLog (workflowdocumentcontent). Till now the two tables
where linked by the fields `document`, `version`, and `workflow` which will
be replaced by the two new fields. The fields `document`, `version`, and
`workflow` will be removed from tblWorkflowLog. tblWorkflowDocumentContent
contained just the workflows currently active for a particlar document.
From now on the table will also contain finished workflows, which
will have the field `state` set to null. This allows to run even the
same workflow again and still be able to distinguish the log entries.

MySQL
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The update process will first add the new auto incrementing, primary
field to tblWorkflowDocumentContent and a referencing field to
tblWorkflowLog. It will then fill out the referencing field with the
automatically incremented field value from tblWorkflowDocumentContent
by joining the two tables with its common fields document, version,
and workflow.  This will not fill out all referencing field values,
because once a workflow has ended the record in
tblWorkflowDocumentContent will be deleted and just the records in
tblWorkflowLog are kept. The still missing records in
tblWorkflowDocumentContent for already completed workflows will be
reconstructed from the records in tblWorkflowLog which do not have a
reference to tblWorkflowDocumentContent yet. Once that is done the
referencing field in tblWorkflowLog can be filled in a second pass.
The date of the new records in tblWorkflowDocumentContent will be
taken from the last record for that workflow in tblWorkflowLog.  The
state of the new records will be set null, indicating that this
workflow is no longer active.

SQLite
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The update process will first create new table for tblWorkflowDocumentContent
containing a new field for the primary key field. It then copies the
records from the old table to the new table. The missing records for
workflows which has been finished already are recreated from the old
table `tblWorkflowLog`. Which is then replaced by a new table having
the foreign key to table `tblWorkflowDocumentContent`.
