Minor file checking optimization: set_dir_cache_file. * lib/Automake/FileUtils.pm (set_dir_cache_file): New function. * automake.in (require_file_internal): Instead of resetting the cache when a file has been installed, simply correct the cache using set_dir_cache_file. Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>