[C++-sig] from python conversions

[Martin Casado]

 I'm trying to rewrite my python to c++ object conversions that 
 I had under the old interface and am running into some problems.

 Am I correct in thinking that we need to use rvalue_from_python
 and lvalue_from_python?  Is there any mechanism similar to
 the old method, in which for a given type_id you can register
 two functions, one to determine whether you can convert the object,
 and the second to do the conversion?

 Thanks,
 Martin