Fix building with newer LUA versions (i.e. fix "openSUSE Factory" build failures)

Changed since last request: Re-diffed gnuplot.changes. (For some reason, there was a gnuplot.changes merge failure despite osc pull - and there was some spurious change in that file. Try again ...)

Builds successfully on oS 12.1 and Factory. 11.4 is unresolvable (texlive issue). SLES 11 fails as texlive-2007 clashes with texlive-bin-2010 (i386) or because of different tex.fmt (mixing different TeX versions, x86-64). SLES 10 fails for epstopdf in ghostscript. All those issues are unrelated to the patch. (forwarded request 104758 from burnus)