Created a new table acq.provider_note, similar to acq.po_note, but tied

Created a new table acq.provider_note, similar to acq.po_note, but tied
to acq.provider instead of to acq.purchase_order.

Also: modified actor.usr_purge_data() to touch the foreign keys to
actor.usr when a user is purged.

M    Open-ILS/src/sql/Pg/999.functions.global.sql
M    Open-ILS/src/sql/Pg/200.schema.acq.sql
M    Open-ILS/src/sql/Pg/002.schema.config.sql
A    Open-ILS/src/sql/Pg/upgrade/0172.schema.acq.provider-notes.sql
M    Open-ILS/examples/fm_IDL.xml

git-svn-id: svn://svn.open-ils.org/ILS/trunk@15640 dcc99617-32d9-48b4-a31d-7c20da2025e4