Automatic testing for generated tlb-files

the test-headers exported by the current `exporter` are tested against a checked-in set of previously generated tlb files. we "just" have to make sure that a correct tlb-export is present in the test-directory and then run the following commands:

    make -C build create-test-header-tlb
    make -C build check-test-header-tlb

this allows us to detect regressions and filter out single differing lines. the cmake-output is a bit verbose due to the cerr-stuff, but hey...