Docs and CI: Work around dnspython Py2/3 idiocy

doc/misc.rst

@@ -21,7 +21,8 @@ Enter the relate directory::
 
     cd relate
 
-Install the dependencies::
+Edit :file:`requirements.txt` to choose a version of `dnspython`, then install
+the dependencies::
 
     pip install -r requirements.txt
 

run-tests-for-ci.sh

 #! /bin/bash
 
+set -e
+
 echo "-----------------------------------------------"
 echo "Current directory: $(pwd)"
 echo "Python executable: ${PY_EXE}"
@@ -54,7 +56,15 @@ export PATH=`pwd`/.env/local/bin:$PATH
 
 PIP="${PY_EXE} $(which pip)"
 
-$PIP install -r requirements.txt
+grep -v dnspython requirements.txt > req.txt
+if [[ "$PY_EXE" = "python2*" ]]; then
+  $PIP install dnspython
+else
+  $PIP install dnspython3
+fi
+
+$PIP install -r req.txt
+
 cp local_settings.py.example local_settings.py
 
 cd test