Rename two config options:

FEATURE_SH_STANDALONE_SHELL => FEATURE_SH_STANDALONE
FEATURE_EXEC_PREFER_APPLETS => FEATURE_PREFER_APPLETS
Make SH_STANDALONE depend on PREFER_APPLETS.
getopt.c: more randomconfig-induced fixes

libbb/default_error_retval.c

@@ -13,7 +13,6 @@
  * that too seems silly.
  */
 
-#include <stdlib.h>
 #include "libbb.h"
 
 int xfunc_error_retval = EXIT_FAILURE;