Merge pull request #517 from whoosh-community/issue-491

Fragment comparison use startchar & endchar, instead of PyObject id

src/whoosh/highlight.py

@@ -152,7 +152,7 @@ def overlapped_length(self, fragment):
         return max(ec, fec) - min(sc, fsc)
 
     def __lt__(self, other):
-        return id(self) < id(other)
+        return self.startchar < other.startchar
 
 
 # Tokenizing