Replace insecure tmpfile() with mkstemp() based local tempfile()

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

exec.c

@@ -179,7 +179,7 @@ int run_interactive(char *cmd, char *fmt, ...)
 	}
 
 	/* Redirect output from cmd to a tempfile */
-	fp = tmpfile();
+	fp = tempfile();
 	if (fp && !debug) {
 		oldout = dup(STDOUT_FILENO);
 		olderr = dup(STDERR_FILENO);