Fixed some issues with text objects in the clipboard.

sugar/datastore/datastore.py

@@ -138,7 +138,8 @@ class DSObject(object):
 
             activityfactory.create(bundle.get_service_name())
         else:
-            if not self.get_activities():
+            if not self.get_activities() and service_name is None:
+                logging.warning('No activity can open this object.')
                 return
             if service_name is None:
                 service_name = self.get_activities()[0].service_name

sugar/objects/mime.py

@@ -81,7 +81,7 @@ def choose_most_significant(mime_types):
         logging.debug('Choosed text/html!')
         return 'text/html'
 
-    if 'text/plain' in mime_types or 'STRING' in mime_types:
+    if 'text/plain' in mime_types:
         logging.debug('Choosed text/plain!')
         return 'text/plain'