This is a patch to a recent checkout of trunk from SVN.
Since the recent revision of partscustomer which changed column
customer_id to credit_id, adding a service to a sales invoice failed with:
DBD::Pg::st execute failed: ERROR: column p.customer_id does not exist
LINE 2: SELECT p.parts_id, p.customer_id AS entity_id,
^ at LedgerSMB/PriceMatrix.pm line 131.
This patch changes the query in LedgerSMB/PriceMatrix.pm to accommodate
the change to the partscustomer table.