pkg/52690: libxml2 fails in python 3.6

[prlw1%cam.ac.uk@localhost]

>Number:         52690
>Category:       pkg
>Synopsis:       libxml2 fails in python 3.6
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Nov 02 15:40:00 +0000 2017
>Originator:     Patrick Welche
>Release:        NetBSD-current/amd64
>Organization:
>Environment:
>Description:
Given:

py36-libxml2-2.9.6  Python wrapper for libxml2

$ python3.6
Python 3.6.3 (default, Oct 27 2017, 17:16:29) 
[GCC 5.4.0] on netbsd8
Type "help", "copyright", "credits" or "license" for more information.
>>> import libxml2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/pkg/lib/python3.6/site-packages/libxml2.py", line 1, in <module>
    import libxml2mod
ImportError: /usr/pkg/lib/python3.6/site-packages/libxml2mod.so: Undefined PLT symbol "PyCObject_Check" (symnum = 488)

The strange part is that PyCObject_Check is only mentioned in the piece of code referred to by textproc/libxml2/patch-python_libxml__wrap.h and is protected by  #if PY_VERSION_HEX < 0x02070000. AFAICT there shouldn't be a PyCObject anywhere.
>How-To-Repeat:

>Fix: