py3: allow SearchResult instances to be hashed

src/calibre/gui2/store/search_result.py

@@ -33,6 +33,9 @@ class SearchResult(object):
     def __eq__(self, other):
         return self.title == other.title and self.author == other.author and self.store_name == other.store_name and self.formats == other.formats
 
+    def __hash__(self):
+        return id(self)
+
     def __str__(self):
         items = []
         for x in 'store_name title author price formats detail_item cover_url'.split():