[tlbuild] dvibook failure on Cygwin

[Karl Berry]

Hi Ken,

    ../../../texk/seetexk/seetexk.test: line 23:  8492 Segmentation fault 
        (core dumped) ./dvibook -s4 playsel.dvi playbook.dvi 2> playbook.2
    FAIL: seetexk.test

I just built the sources on my usual i386-linux and seetexk.test passed.
Sorry :).

k