Patch: fix ColName in db-schema.xml

The following patch fixes a ColName attribute in the db schema, from visit_exit_idaction to visit_exit_idaction_url.

IIRC this was required during some upgrade, but I cannot say if it still applies (and/or is wrong).

Therefore, please verify this carefully, before applying.

Thanks.

The schema is out-of-date in other places. I’ll create a ticket in Trac.