[C++-sig] Boost.Python v2: More interface-breaking changes

[David Abrahams]

More of the interface has been changed to use object instead of handle<>,
as part of the work on docstring support.
Major changes:

* object(f), where f is a function pointer now works. Returning a
  function pointer from a function should work also.
* make_function/make_constructor now return object instead of a raw
pointer.
* module::setattr() now accepts anything which can be passed to object's
constructor.

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           David Abrahams * Boost Consulting
dave at boost-consulting.com * http://www.boost-consulting.com