Schema/behavior tweak

Since transaction_item has a price field, for the purposes of this
application, there is no reason to keep old versions of items around.
((each item in a transaction will have a price permanently associted
with it.))
Experimental transaction support.

Needs more testing, but it seems to work. Now, if any sql fails inside
an addeditview save call, all changes made inside that save call should
be rolled back.