** New files:
* Comes with config.sub and config.guess.
* Uses config.h.bot if present, analogous to config.h.top.
+* Uses config.cache to cache test results. An alternate cache file
+ can be selected with the --cache-file=FILE option.
** New macros:
+* AC_CACHE_USE to share results of tests between configure runs.
* AC_CONFIG_AUX, AC_SYSTEM_TYPE, AC_SUBST_FILE, AC_MAKE_LINKS to
support deciding unguessable features based on the host and target types.
* AC_CONFIG_SUBDIRS to recursively configure a source tree.