Fix copy-and-pasteo that's causing pg_regress to lie about which file it can't

read when the --temp-config argument is bad.  Noted while wondering why
buildfarm member dungbeetle is failing ... this isn't why, but it is why
the error report isn't very helpful ...

src/test/regress/pg_regress.c

@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/test/regress/pg_regress.c,v 1.45 2008/05/17 20:02:01 tgl Exp $
+ * $PostgreSQL: pgsql/src/test/regress/pg_regress.c,v 1.46 2008/08/03 05:12:38 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2079,7 +2079,7 @@ regression_main(int argc, char *argv[], init_function ifunc, test_function tfunc
 			extra_conf = fopen(temp_config, "r");
 			if (extra_conf == NULL)
 			{
-				fprintf(stderr, _("\n%s: could not open %s to read extra config:\nError was %s\n"), progname, buf, strerror(errno));
+				fprintf(stderr, _("\n%s: could not open %s to read extra config:\nError was %s\n"), progname, temp_config, strerror(errno));
 				exit_nicely(2);
 			}
 			while (fgets(line_buf, sizeof(line_buf), extra_conf) != NULL)