[C++-sig] from_python non-compiletime-constant

[Neal Becker]

I need to register a from_python conversion where the type object is not a
compile constant.  I'm trying to write c++ code that will accept a numpy
array.

AFAICT, the PyTypeObject addresses aren't known at compile time, so can't be
used in lvalue_from_pytype template arguments.  These pointers can be found
at runtime.  How do I handle this?