support optional to condition to *list

tests/dictionaries/80target_list_unknown/00-base.xml

@@ -0,0 +1,15 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<rougail>
+    <variables>
+        <variable name="condition" type="boolean"/>
+    </variables>
+
+    <constraints>
+        <condition name="disabled_if_in" source="condition">
+            <param>True</param>
+            <target type="filelist">unknown</target>
+        </condition>
+    </constraints>
+</rougail>
+<!-- vim: ts=4 sw=4 expandtab
+-->