sensors-detect: Detect incorrect non-interactive runs

It is better to use option --auto for non-interactive runs of the
sensors-detect script than faking an input to get the default answers
to all questions.

CHANGES

@@ -11,6 +11,7 @@ SVN HEAD
                   Add detection of F71868A
                   Add a PCI ID for new family 15h AMD processors
                   Introduce automatic mode (--auto)
+                  Detect incorrect non-interactive runs
 
 3.3.4 (2013-05-27)
   sensors.conf.5: Mention "sensors -u" to get the raw feature names

prog/detect/sensors-detect

@@ -2517,7 +2517,7 @@ sub read_answer
 		print "\n";
 		return "";
 	}
-	return <STDIN>;
+	return <STDIN> || "";
 }
 
 ###################
@@ -7012,6 +7012,15 @@ sub main
 	}
 
 	unload_modules();
+
+	# Check if running non-interactively without --auto
+	if (!$opt{auto} && ! -t STDIN) {
+		print "***************************************************************\n".
+		      "Warning: the preferred way to run this script non-interactively\n".
+		      "is with option --auto. Other methods are discouraged and may\n".
+		      "stop working at some point in the future.\n".
+		      "***************************************************************\n\n";
+	}
 }
 
 sub cleanup_on_int