[Dev-luatex] cygwin static detection

Hello, The attached patch detects if LuaTeX is compiled under cygwin: the result of os.type is unix and os.name is cygwin. Without this patch, os.type is unix and os.name is generic... Is this patch ok or would you prefer os.type to return windows? I think it's best this way. Anyway, as most users will use binaries compiled under non-cygwin in their cygwin system, thus it does not solve the cygwin detection problem. Thank you, -- Elie