Extend full stack PDF tests to contain hyperlinks with underscores.

Related to https://github.com/4teamwork/ftw.pdfgenerator/pull/35
This tests that the PDF can be built with internal as well as external hyperlinks contianing underscores.
Merge pull request #70 from 4teamwork/jone-hyperlinks-with-underscores

Extend full stack PDF tests to contain hyperlinks with underscores.