Dropping and recreating a foreign key constraint for config.metabib_field,

Dropping and recreating a foreign key constraint for config.metabib_field,
in order to change its name.  WHen this foreign key was first introduced,
the upgrade script gave it one name and the base install script gave it
a different name.  Here we bring the names into sync.

M    Open-ILS/src/sql/Pg/002.schema.config.sql
A    Open-ILS/src/sql/Pg/upgrade/0415.schema.rename-field-class-fkey.sql

git-svn-id: svn://svn.open-ils.org/ILS/trunk@17915 dcc99617-32d9-48b4-a31d-7c20da2025e4