EPUB metadata: When extracting covers from epub files handle invalid epubs that specify their content as a raster cover. Apparently PG produces these.

src/calibre/ebooks/metadata/opf2.py

@@ -966,7 +966,9 @@ class OPF(object): # {{{
             cover_id = covers[0].get('content')
             for item in self.itermanifest():
                 if item.get('id', None) == cover_id:
-                    return item.get('href', None)
+                    mt = item.get('media-type', '')
+                    if 'xml' not in mt:
+                        return item.get('href', None)
 
     @dynamic_property
     def cover(self):

src/calibre/gui2/actions/choose_library.py

@@ -246,7 +246,7 @@ class ChooseLibraryAction(InterfaceAction):
     def delete_requested(self, name, location):
         loc = location.replace('/', os.sep)
         if not question_dialog(self.gui, _('Are you sure?'), '<p>'+
-                _('All files from %s will be '
+                _('<b>All files</b> from %s will be '
                 '<b>permanently deleted</b>. Are you sure?') % loc,
                 show_copy_button=False):
             return