exit with error if stdout isatty()

ChangeLog

@@ -1,5 +1,6 @@
 2010-02-10 m. allan noah <kitno455 at gmail dot com>
 	* acinclude.m4, configure: missing $ in variable expansion
+	* frontend/scanimage.c: exit with error if stdout isatty()
 
 2010-02-10 m. allan noah <kitno455 at gmail dot com>
 	* backend/cardscan.[ch], backend/cardscan.conf.in,

frontend/scanimage.c

@@ -2208,6 +2208,11 @@ List of available devices:", prog_name);
 		 "Scanning %d pages, incrementing by %d, numbering from %d\n",
 		 batch_count, batch_increment, batch_start_at);
 
+      else if(isatty(fileno(stdout))){
+	fprintf (stderr,"%s: output is not a file, exiting\n", prog_name);
+        exit (1);
+      }
+
       do
 	{
 	  char path[PATH_MAX];