Message 56336 - Python tracker

This patch removes the buffer API from PyUnicode, as specified by PEP
3137. All the unit tests passes. However, I believe there is a few
function calls to PyArg API that could become problematic if they are
given a PyUnicode object:

  % egrep -R --include='*.c' 'PyArg.*Parse.*"[^;:]*[cwt].*"' py3k/

I haven't checked these function calls yet. So, it would probably be a
good idea to wait I do so before committing this patch.