Change the GHCi monad from type

	GHCiState -> IO (GHCiState, a)
to
	IORef GHCiState -> IO a

to avoid losing recent changes to the state when we receive an
exception (which would normally be harmless, except that the state
isn't purely functional: it must match some state kept by the RTS's
dynamic linker).  Asynchonous exceptions could still cause us some
difficulty.