Add action hooks to wp-activate.php in WP network

[gdvwp]

Similar to the hooks in wp-signup.php:

do_action( 'before_signup_form' );
do_action( 'after_signup_form' );

these hooks should be added to wp-activate.php:

do_action( 'before_activate_form' )
do_action( 'after_activate_form' )

Purpose : allow signup and activate pages to be built/styled in a similar way.