New feature: Site Policy Agreements.

If the admin specifies a Policy Agreement (via URL in the config variables)
then each user is required to see and agree to that document once before
continuing.

To get everyone to see it again (on an update, say) one just needs to issue:

   UPDATE user SET policyagreed = 0

lib/db/postgres7.sql

@@ -223,6 +223,7 @@ CREATE TABLE prefix_user (
    id SERIAL PRIMARY KEY,
    auth varchar(20) NOT NULL default 'manual',
    confirmed integer NOT NULL default '0',
+   policyagreed integer NOT NULL default '0',
    deleted integer NOT NULL default '0',
    username varchar(100) NOT NULL default '',
    password varchar(32) NOT NULL default '',