Heavily reworked the usage of the db link: Oracle does not provide

marshalling of arrays or custom types over a db link, hence temporary
tables are used to transfer the data and read back the results.
Also introduced a serrno PL/SQL package in both the NS and Stager
databases.
Adapted the OCCI interface to match the PL/SQL procedure for migration,
still some modifications to be done (the bulk methods don't return anything)
prior to start testing.