Acq invoices - Use build_invoice_impl() instead of creating directly

Acq invoices - Use build_invoice_impl() instead of creating directly

In this way we use the same logic in both creating EDI invoices and
creating them from user input to do two things in particular:

1) always disencumber fund debits (used to be done in manual process only
and not EDI)

2) automatically uncancel the necessary canceled copies if you're
invoicing them anyway, since they must have shown up after all
(especiallly important since "cancelled" [sic] in our schema includes
copies merely back-ordered) (used to be done in EDI only and
not the manual process)

Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>