updating to 2.6.4 - for detailed commits see https://github.com/jeckman/wpbook

git-svn-id: https://plugins.svn.wordpress.org/wpbook/trunk@759314 b8457f37-d9ea-0310-8a92-e5e31aec5664
oops - tab.php is in that release too

git-svn-id: https://plugins.svn.wordpress.org/wpbook/trunk@759315 b8457f37-d9ea-0310-8a92-e5e31aec5664