redeclaration of builtin types, followup for #170

[robertwb]

More work needs to be done to allow subclassing/attribute access from builtin types. See #170.

[scoder]

Pyrex is supposed to handle the subtyping part correctly, so this needs a port.

 http://comments.gmane.org/gmane.comp.python.cython.devel/5552

[scoder]

... running out of time before even getting started.

The relevant commits in Pyrex are at revision 26-37 in  http://hg.cython.org/pyrex/

Porting this will likely interfere with Cython's builtin caching feature, although that might become redundant in many cases. True/False handling is another thing that works different in Cython now, so that must be left out.

[scoder]

This isn't trivial, so it won't happen for 0.12, I guess.

[robertwb]

There is now a warning for redecoration of builtin types. This creates a new type, on the same level with all other extern types, which may have attributes and accept subclasses, and does *not* perform the optimizations associated with the builtin one. Assignment from the builtin type is allowed, e.g.

cdef extern from "Python.h":
    ctypedef class __builtin__.list  [object PyListObject]:
        cdef Py_ssize_t allocated

cdef list L = [1,2,4]
print L. allocated

Such redeclarations are still discouraged.

 http://hg.cython.org/cython-devel/rev/64ffae746f98

 http://hg.cython.org/cython-devel/rev/2de0e2c7a09a