immler@in.tum.de [Mon, 04 May 2009 23:37:39 +0200] rev 31037
added Philipp Meyer's implementation of AtpMinimal
together with related changes in the sledgehammer-interface:
adapted type of prover, optional relevance filtering,
public get_prover for registered atps in AtpManager,
included atp_minimize in s/h response;