Make Document and DocumentFragment stringify better

Having both __str__ and __unicode__ appears to be necessary to
handle both explicit print and when a value is echoed in
an interactive python shell.

http://code.google.com/p/html5lib/issues/detail?id=169

Author: foolip

html5lib/treebuilders/simpletree.py

@@ -83,9 +83,12 @@ class Document(Node):
     def __init__(self):
         Node.__init__(self, None)
 
-    def __unicode__(self):
+    def __str__(self):
         return "#document"
 
+    def __unicode__(self):
+        return str(self)
+
     def appendChild(self, child):
         Node.appendChild(self, child)
 
@@ -112,9 +115,12 @@ def cloneNode(self):
 
 class DocumentFragment(Document):
     type = 2
-    def __unicode__(self):
+    def __str__(self):
         return "#document-fragment"
 
+    def __unicode__(self):
+        return str(self)
+
     def cloneNode(self):
         return DocumentFragment()