Issues when creating/modifying objects with dbi backend

[Phil Longstaff]

Now that there is an sql backend which saves changes immediately, care
needs to be taken when creating or modifying objects.  In general, using
a begin-edit/commit-edit block will reduce the number of commits, but
will also prevent problems.  As an example of the kind of problems,
there are currently some non-null constraints on some columns.  If you
create a lot, for example, and then set the title outside of a
begin-edit/commit-edit block, the save will fail because there is a
not-null constraint on the account, and it hasn't been set yet.  This is
exactly the problem I need to fix when posting an invoice.

Phil