Add test for --ignore-directory=$bad_directory

This addresses issue #7

t/ignore-bad-dir.t

@@ -0,0 +1,19 @@
+use strict;
+use warnings;
+use lib 't';
+
+use Test::More tests => 2;
+use Util;
+
+IGNORE_DIR_NO_PERMS: {
+    mkdir 't/swamp/.ignoreme';
+    chmod 000, 't/swamp/.ignoreme';
+
+    my @args  = ( '--ignore-directory=is,.ignoreme', '-l', 'FOO' );
+    my @files = 't/swamp';
+
+    my ( $stdout, $stderr ) = run_ack_with_stderr( @args, @files );
+    rmdir 't/swamp/.ignoreme';
+    is @{$stderr}, 1 or diag(explain($stderr));
+    like $stderr->[0], qr!ack: t/swamp/.ignoreme:!;
+}