DOCX export: XPath should allow checking for the number of returned nodes.
DOCX export: XPath should allow checking for the number of returned nodes.

This is to implement a test that <w:next> style is not exported for styles
where the next style equals to the style itself [which comes with this commit
too].

Change-Id: I5fa9999cf7e741dc96f3538b7c1106e1add6b61e

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