Load phpCAS Library Based on class_exists( )

Load the phpCAS library from the
$wp_cas_ldap_use_options['include_path'] configuration array path if
class_exists( ) fails to find the class name 'phpCAS' already defined in
the environment. Also call the phpCAS::client method if class phpCAS
does not exsist and assume that phpCAS::client has already been called
if the class does exsist.