Improve error messages for the xml-diff based unit tests.
Improve error messages for the xml-diff based unit tests.

Change-Id: Ided6749ebe4899a6d826d069c38d7b21b467d431

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core