Merge pull request #5993 from mlkwaqas/waqas/tnl752-discussion-id-should-be-unique

Advanced settings discussion category ids should be unique.

common/lib/xmodule/xmodule/course_module.py

@@ -260,7 +260,7 @@ class CourseFields(object):
     )
     discussion_topics = Dict(
         display_name=_("Discussion Topic Mapping"),
-        help=_("Enter discussion categories in the following format: \"CategoryName\": {\"id\": \"i4x-InstitutionName-CourseNumber-course-CourseRun\"}. For example, one discussion category may be \"Lydian Mode\": {\"id\": \"i4x-UniversityX-MUS101-course-2014_T1\"}."),
+        help=_("Enter discussion categories in the following format: \"CategoryName\": {\"id\": \"i4x-InstitutionName-CourseNumber-course-CourseRun\"}. For example, one discussion category may be \"Lydian Mode\": {\"id\": \"i4x-UniversityX-MUS101-course-2014_T1\"}. The \"id\" value for each category must be unique."),
         scope=Scope.settings
     )
     discussion_sort_alpha = Boolean(