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/execable.c

@@ -60,7 +60,7 @@ int exists_execable(const char *filename)
 	return 0;
 }
 
-#if ENABLE_FEATURE_EXEC_PREFER_APPLETS
+#if ENABLE_FEATURE_PREFER_APPLETS
 /* just like the real execvp, but try to launch an applet named 'file' first
  */
 int bb_execvp(const char *file, char *const argv[])