needed output.validsource for DocBook XML xmllint validation

tldp/outputs.py

@@ -59,6 +59,10 @@ class OutputNamingConvention(object):
     def name_indexhtml(self):
         return os.path.join(self.dirname, 'index.html')
 
+    @property
+    def validsource(self):
+        return os.path.join(self.dirname, self.stem + '.xml')  # -- burp
+
     @property
     def iscomplete(self):
         '''True if the output directory contains all expected documents'''