config: Reassemble strings sensibly

If a string-based configuation entry had whitespace in it, it would be
reassembled via a round-trip through the python interpreter, resulting
in a line like this:

    PidFile /home/dkimpy-milter/pid file

produces a string like "['/home/dkimpy-milter/pid', 'file']", which is
clearly wrong.

I don't want to encourage people to use paths or other strings with
whitespace in them, but if we're going to fail on them we should be
failing explicitly, not doing a weird transformation that will just
break.

This is concretely useful for the DNSOverride mechanism, which is
where i ran into the problem when trying to set up testing that could
work without setting up an emulated DNS system.

dkimpy_milter/config.py

@@ -390,7 +390,10 @@ def _readConfigFile(path, configData=None, configGlobal={}):
         if conversion == 'bool':
             configData[name] = _find_boolean(value)
         elif conversion == 'str':
-            configData[name] = str(value)
+            if isinstance(value, list):
+                configData[name] = line.split(None, 1)[1]
+            else:
+                configData[name] = str(value)
         elif conversion == 'int':
             configData[name] = int(value)
         elif conversion == 'dataset':