Merge from trunk

src/calibre/devices/usbms/books.py

@@ -59,7 +59,7 @@ def fget(self):
         return property(doc=doc, fget=fget)
 
     @dynamic_property
-    def thumbnail(self):
+    def thumbnail(self):'
         return None
 
 class BookList(_BookList):

src/calibre/ebooks/metadata/book/__init__.py

@@ -110,7 +110,7 @@
                            frozenset(['title', 'title_sort', 'authors',
                                       'author_sort', 'author_sort_map' 'comments',
                                       'cover_data', 'tags', 'language', 'lpath',
-                                      'size'])
+                                      'size', 'thumbnail'])
 
 SERIALIZABLE_FIELDS =      SOCIAL_METADATA_FIELDS.union(
                            USER_METADATA_FIELDS).union(

src/calibre/ebooks/metadata/book/base.py

@@ -243,7 +243,7 @@ def copy_not_none(dest, src, attr):
                 lotags = [t.lower() for t in other.tags]
                 lstags = [t.lower() for t in self.tags]
                 ot, st = map(frozenset, (lotags, lstags))
-                for t in st.interection(ot):
+                for t in st.intersection(ot):
                     sidx = lstags.index(t)
                     oidx = lotags.index(t)
                     self.tags[sidx] = other.tags[oidx]