Fix #11415: Check executable bit on admin/ folder, not readable bit

login_page has a check that warns if the admin/ folder is still in
place. However this check uses is_readable() instead of is_executable().
In the case of folders, the read bit determines who can list the
directory. The execute bit determines who can traverse and access files
within the directory.

Signed-off-by: David Hicks <hickseydr@optusnet.com.au>

login_page.php

@@ -210,7 +210,7 @@
 
 	# Check if the admin directory is available and is readable.
 	$t_admin_dir = dirname( __FILE__ ) . DIRECTORY_SEPARATOR . 'admin' . DIRECTORY_SEPARATOR;
-	if ( is_dir( $t_admin_dir ) && is_readable( $t_admin_dir ) ) {
+	if ( is_dir( $t_admin_dir ) && is_executable( $t_admin_dir ) ) {
 		echo '<div class="warning" align="center">', "\n";
 		echo '<p><font color="red">', lang_get( 'warning_admin_directory_present' ), '</font></p>', "\n";
 		echo '</div>', "\n";