- enabled giving simple class as base class parameter again

- removed unnecessary template argument from base class "conversion_policy"
- brought conversion policies in line with that change
- added "policy_list", "no_policies" and "no_bases" aliases to the luabind namespace (note that policy_list is still problematic on MSVC)
Merge branch 'master' of https://github.com/decimad/luabind-deboostified