Master - saving to xml broken

[Geert Janssens]

Hi,

The last couple of days I find that the master branch breaks xml files during 
save. I didn't report earlier because I had to check first whether it wasn't 
due to my own branch.

Built a clean current master today, and it still saves broken xml data files.

The error message is - as usual with the backend - pretty vague:
* 13:27:04  WARN <gnc.backend> [GncXmlBackend::load()] Syntax error in Xml 
File /home/janssege/Development/gnucash/testdata/KobaltTest.xac

To reproduce: open a working file and save it as xml. For my test I simply 
added and remove one character of one single transaction description and then 
saved the file again.

Analyzing the broken file I find:
1. there are several duplicate xml namespaces in the xmlns list: billterm, bt-
days, bt-prox, cust, employee, entry, invoice, job, order, taxtable, tte, 
vendor and addr. They were in the original file as well, but only once.

2. gnc:count-data equally has a number of duplicate entries, also for business 
objects only.

3. The original book only had gnc:commodity entries for currencies that are 
really in use. The new book has an entry for each commodity we support.

4. all objects that didn't have slots before, now have an empty slots xml 
entity. The commodities now have for example <cmdty:slots/>. Similarly there 
are now also plenty of empty entities for accounts, transactions, splits, ...

This issue must have been introduced before commit dd4b8a104d0f7 on master. 
That's the commit my cpp branch branches off from and I'm seeing it there as 
well (albeit with a slightly different error message:* 10:54:04  WARN 
<gnc.backend> [gnc_xml_be_load_from_file()] Syntax error in Xml File /home/
janssege/Development/gnucash/testdata/KobaltTest.xac)

Regards,

Geert