python3-docutils: add explicit Breaks: python-docutils

the existing implicit Breaks via the versioned dependency on
docutils-common is not sufficient for all upgrade paths

Closes: #986871.

debian/changelog

@@ -12,6 +12,10 @@ python-docutils (0.16+dfsg-4) UNRELEASED; urgency=low
   * d/control: Update Vcs-* fields with new Debian Python Team Salsa
     layout.
 
+  [ Andreas Beckmann ]
+  * python3-docutils: Add explicit Breaks: python-docutils for smoother
+    upgrades from buster.  (Closes: #986871)
+
  -- Debian Janitor <janitor@jelmer.uk>  Wed, 02 Sep 2020 07:19:45 -0000
 
 python-docutils (0.16+dfsg-3) unstable; urgency=medium

debian/control

@@ -29,6 +29,7 @@ Suggests: docutils-doc,
           texlive-lang-french,
           texlive-latex-base,
           texlive-latex-recommended
+Breaks: python-docutils (<< 0.16+dfsg-3)
 Description: text processing system for reStructuredText (implemented in Python 3)
  reStructuredText is an easy-to-read, what-you-see-is-what-you-get plaintext
  markup syntax and parser system. It is useful for in-line program documentation