Revert use of config.h

Revert
7162e8db74
088493d499

And drop AC_CONFIG_HEADERS so that config goes though the command line.
No longer generating config.h, update .gitignore

src/libmdb/write.c

@@ -16,7 +16,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
-#include "config.h"
 #include <time.h>
 #include <math.h>
 #include <inttypes.h>