ORDRSP processing - PO linkage and object refresh

ORDRSP processing - PO linkage and object refresh

Several objects get updated potentially several times during processing,
and it is important to retrieve the item after earlier updates because
some columns are being populated by DB default values or 'NOW', for example.
The first 'NOW' for create_time would be correct, the subsequent ones incorrect,
so the value(s) must be fetched.

In order that an edi_message shows up in the list associated with a PO, we take the
first valid PO number, if present.  Note that this mapping theoretically may vary:
multliple PO lineitems *could* appear in one response, but in practice, we
expect only one, so this should suffice.  This is also a good reason to prevent
splitting a PO after it has been sent.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@17690 dcc99617-32d9-48b4-a31d-7c20da2025e4