Added error message for questions descriptions not unique. 	Change on 2013/06/27 by juliaoh <juliaoh@google.com> ------------- Created by MOE: http://code.google.com/p/moe-java MOE_MIGRATED_REVID=48649899
Added error message for questions descriptions not unique.
	Change on 2013/06/27 by juliaoh <juliaoh@google.com>
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=48649899

andela-angene/coursebuilder-core,andela-angene/coursebuilder-core,andela-angene/coursebuilder-core,andela-angene/coursebuilder-core