3.6: python3 incompatibility crashes the build on linux

Hello

build of latest 3.6 fails for me when python3 is enabled with:

    ----8<----
    /usr/bin/ld: ../python/3/libmu_py/.libs/libmu_py.so: undefined reference to `PyString_FromString'
    /usr/bin/ld: ../python/3/libmu_py/.libs/libmu_py.so: undefined reference to `PyInt_FromLong'
    collect2: error: ld returned 1 exit status
    make[4]: *** [Makefile:1152: maidag] Error 1
    make[4]: Leaving directory '/home/balducci/tmp/install-us-d/mailutils-3.5.90.d/mailutils-3.6/maidag'
    ---->8----

It turns out that PyString_FromString and PyInt_FromLong aren't in
python3's API (at least 3.5.5<=python3<=3.8.0a1, the
versions I could try) and should be replaced by PyUnicode_FromString
and PyLong_FromLong, resp. The following crude workaround fixes the
build for me

    ----8<----
    diff -c python/3/libmu_py/mailcap.c.FIX_MAILCAP_C python/3/libmu_py/mailcap.c
    *** python/3/libmu_py/mailcap.c.FIX_MAILCAP_C	Sun Feb 24 10:53:17 2019
    --- python/3/libmu_py/mailcap.c	Sun Feb 24 10:53:17 2019
    ***************
    *** 1,3 ****
    --- 1,6 ----
    + #define  PyString_FromString  PyUnicode_FromString
    + #define  PyInt_FromLong       PyLong_FromLong
    + 
      /* GNU Mailutils -- a suite of utilities for electronic mail
         Copyright (C) 2009-2019 Free Software Foundation, Inc.
    ---->8----

My specs:

install:156> uname -ar
Linux  4.20.10 #1 SMP Sun Feb 17 14:34:36 CET 2019 x86_64 GNU/Linux

install:157> gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/stow.d/versions/gcc-8.2.0/usr/lib64/gcc/x86_64-pc-linux-gnu/8.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /home/balducci/tmp/install-us-d/gcc-8.2.0.d/gcc-8.2.0/configure --prefix=/opt/stow.d/versions/gcc-8.2.0/usr --libdir=/opt/stow.d/versions/gcc-8.2.0/usr/lib64 --libexecdir=/opt/stow.d/versions/gcc-8.2.0/usr/lib64 --enable-shared --disable-bootstrap --enable-languages=c,c++,objc,fortran --enable-multilib
Thread model: posix
gcc version 8.2.0 (GCC) 

install:158> python --version
Python 3.8.0a1

ciao
-g