0014998: Invoices should have doc number assigned when they are completed, not when they are saved for the 1st time

Description

There should be an option that allows an Invoice's "Document Number" to be assigned based on the document type sequence only when the invoice is completed, and not when the document is saved.
These documents are important, and should be easily accounted for. If they are meant to be sequential, it doesn't make sense that an user can simply create a invoice draft, save it, and then delete it, thus skipping numbers in that sequence.
Also, the sequence should reflect the invoice completion date, ie, the date the invoice was officially created (completed). Before completion, an invoice should just be an internal draft, and thus shouldn't share the same numbering sequence as the official documents
This restrictions must be met by law in Portugal, and probably in other countries, but I believe that they make sense in many other scenarios, and should make it easier for every company to distinguish drafts from complete, final invoices.

Steps To Reproduce

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Proposed Solution

On save, before completion, use an alternate, temporary and officially irrelevant sequence as document number in invoices. The document sequence number associated with the document type should only be used when the invoice is completed

Issue History
Date Modified	Username	Field	Change
2010-10-22 17:14	tgarcia	New Issue
2010-10-22 17:14	tgarcia	Assigned To	=> adrianromero
2010-10-22 17:47	vfaroque	Issue Monitored: vfaroque
2011-06-03 10:58	dalsasua	Assigned To	adrianromero => dalsasua
2011-07-20 18:13	dalsasua	Assigned To	dalsasua => jonalegriaesarte

Relationships [ Relation Graph ] [ Dependency Graph ]

Notes
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