*: mass renaming of USE_XXXX to IF_XXXX

and SKIP_XXXX to IF_NOT_XXXX - the second one was especially
badly named. It was not skipping anything!

coreutils/df.c

@@ -64,9 +64,9 @@ int df_main(int argc, char **argv)
 	opt_complementary = "k-m:m-k";
 #endif
 	opt = getopt32(argv, "kP"
-			USE_FEATURE_DF_FANCY("aiB:")
-			USE_FEATURE_HUMAN_READABLE("hm")
-			USE_FEATURE_DF_FANCY(, &chp));
+			IF_FEATURE_DF_FANCY("aiB:")
+			IF_FEATURE_HUMAN_READABLE("hm")
+			IF_FEATURE_DF_FANCY(, &chp));
 	if (opt & OPT_MEGA)
 		df_disp_hr = 1024*1024;