Increase support for serials in Evergreen.

Increase support for serials in Evergreen.

The attached patch does the following:

Extends and modifies the serials schema:
 * adds a serial.record_entry (sre) and associated serial.full_rec table for storing MFHD records and their corresponding flattened representation; sre currently links to a bib record
 * makes serial.subscription.end_date nullable to represent current subscriptions in a simpler fashion; whereas the intent expressed at http://open-ils.org/dokuwiki/doku.php?id=acq:serials:model had been to have one subscription per year, it might be easier (at least for migrating existing data) to generate a single subscription record with a start_date representing the start of holdings and end_date null to indicate that the subscription is current (still receiving issues)
 * adds serial.issuance.location to give issuances the ability to have a shelving location without having a barcode
 * links the serial.*_summary tables to serial.subscription rather than to asset.call_number; serial.subscription already has a link to asset.call_number, and the existing DDL actually references serial.subscription even though the column name is "call_number"

 * adds IDL for the serials schema
 * adds a vestigial OpenILS::Application::Ingest::Serial package for ingesting serial records
 * adds a marc2sre.pl import script for generating sre JSON records, based on the MFHD generated by our system

git-svn-id: svn://svn.open-ils.org/ILS/trunk@12655 dcc99617-32d9-48b4-a31d-7c20da2025e4