# File mk, line 480
def tryfile(dir,base,tried)
  extensions = [File.extname(base)]
  if extensions[0].empty?
    extensions = %w{.tex .ltx .drv .dtx}
  else
    base = File.basename(base,'.*')
  end
  extensions.each do |ext|
    tried.push(file = "#{dir}/#{base}#{ext}")
    warn("Input file - trying #{file}") if @verbose
    return [dir,base,ext,file] if File.exist?(file)
  end
  return nil
end