Fixed a problem with the public role removal

I committed a change to the RoleBooster that fixes a stupid but hard to find problem with the public role removal. Now the Role Booster can correctly remove a role from an agent proxy returning the "un-roled" version of the proxy.

Interestingly the Role Booster was not behaving nicely with a single role case: if an agent assumes a single role, and then wants to immediatly discard it, the booster was continuing to return the same proxy instance (or better, a new one cloned from the current one). For this reason now, when only the role interface is found on the current proxy, the instance returned is a superclass. This is fine with WhiteCat because the Role Booster guarantees that each "roled" proxy is a subclass of the starting proxy class, so the inheritance chain is growing to the bottom.