position of privatemsg_invoke_privatemsg

At the moment privatemsg_invoke_privatemsg($message, 'sent'); is called in privatemsg_new_form_submit().

that means, that if sb calls the api function to send a privatemsg, the invoke function is not called (-> _privatemsg hook is not called)

i would propose to put it into _privatemsg_send. (where the pm is really send)