Add a cancel_reason column to acq.user_request, pointing to acq.cancel_reason.

Add a cancel_reason column to acq.user_request, pointing to acq.cancel_reason.

Also: corrected the IDL entries for similar columns elsewhere.  The <link>
should have a reltype of "might_have", not "has_a", since the column is nullable.

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/0181.schema.acq-user-request-cancel-cause.sql
M    Open-ILS/examples/fm_IDL.xml

git-svn-id: svn://svn.open-ils.org/ILS/trunk@15733 dcc99617-32d9-48b4-a31d-7c20da2025e4