wenzelm [Fri, 03 Oct 2008 19:35:17 +0200] rev 28484
misc simplifcation and tuning;
no export of structure Provers;
added add_provers, print_provers;
operate on Proof.state, not Toplevel.state;
use Time.+ etc. to make SML/XL of NJ happy;
explicit Isar commands 'atp_kill', 'atp_info', 'print_atps';