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Allows admins to define a set of "roles" for easier player privilege
management.

The role command (re)defines a role as a set of privs:
	/role <role> priv,priv,priv
Each priv can be a primitive priv or a role name.  Role names
will be expanded at the time they're applied, so redefining a role
that other roles depend on may affect all dependant roles.

There are a few special built-in roles:
	all - all privileges
	none - remove all existing privileges
	default - the set of privileges assigned to new players
The built-in roles cannot be redefined.

/grant and /grantme can be used to grant roles the same as privs.
First, all roles are expanded into their privs.  If the "none" role
is included, then it's applied before any other privs.

Revoking a role effectively revokes all privs it grants.

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