start splitting out readonly values from AnnexState

Values in AnnexRead can be read more efficiently, without MVar overhead.
Only a few things have been moved into there, and the performance
increase so far is not likely to be noticable.

This is groundwork for putting more stuff in there, particularly a value
that indicates if debugging is enabled.

The obvious next step is to change option parsing to not run in the
Annex monad to set values in AnnexState, and instead return a pure value
that gets stored in AnnexRead.

Assistant/TransferSlots.hs

@@ -91,9 +91,9 @@ runTransferThread' mkcheck rt d run = go
   where
 	go = catchPauseResume $ do
 		p <- runAssistant d $ liftAnnex $ 
-			Annex.getState Annex.transferrerpool
+			Annex.getRead Annex.transferrerpool
 		signalactonsvar <- runAssistant d $ liftAnnex $
-			Annex.getState Annex.signalactions
+			Annex.getRead Annex.signalactions
 		withTransferrer' True signalactonsvar mkcheck rt p run
 	pause = catchPauseResume $
 		runEvery (Seconds 86400) noop