Refactor \pdfstrcmp test slightly so that text is not repeated

This means we have the same text automatically in format and package mode.
It also highlights some other issues: further checkins to come!


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4639 de43f980-851b-0410-b2f7-c40aca1f87e0