Bz967609 - fix the cached value reading + replace corrupted dtable with correct one

I replaced corrupted dtable that has been used to test the external link (and cached value) resolution with correct one created using Excel and not Libre(Open)Office. The dtable contains broken link, but also cached value which should be resolved in this case. All tests pass.

I also updated the Excel parser a bit so that the cached String value if read if the external link resolution fails.

I will discuss the changes with @mariofusco once he's back from JavaZone.