First pass at "save as" functionality for GDA backends

[Phil Longstaff]

I've just committed the first pass at the "save as" functionality for GDA backends.  I am concentrating on the backend at this point, not on proper integration into menus and the "save as" dialog.  Under "Save" and "Save as" in the file menu, I've added "Save as GDA".  You need to have "gnucash" set up using the GDA config tools as a data source.  I've only tested it with a mysql db engine, but it should work with other engines as well.  It stores accounts and prices from the pricedb as well as their commodities.  Transactions will come next, then sched transactions and budgets.  I still have done no work on the business objects.

Phil