fix fastDebug to check if debugging is actually enabled

Had to add to AnnexRead an indication of whether debugging is enabled.

Could have just made setupConsole not install a debug output action that
outputs, and have enableDebug be what installs that, but then in the
common case where there is no debug selector, and so all debug output is
selected, it would run the debug output action every time, which entails
an IORef access. Which would make fastDebug too slow..

CmdLine.hs

@@ -142,14 +142,14 @@ subCmdName argv = (name, args)
 		| otherwise = (Just a, reverse c ++ as)
 
 -- | Note that the GlobalSetter must have already had its annexReadSetter
--- applied before entering the Annex monad; that cannot be changed while
--- running in the Annex monad.
+-- applied before entering the Annex monad to run this; that cannot be
+-- changed while running in the Annex monad.
 prepRunCommand :: Command -> GlobalSetter -> Annex ()
 prepRunCommand cmd globalsetter = do
 	when (cmdnomessages cmd) $
 		Annex.setOutput QuietOutput
 	annexStateSetter globalsetter
-	whenM (annexDebug <$> Annex.getGitConfig) $
+	whenM (Annex.getRead Annex.debugenabled) $
 		enableDebugOutput
 
 findAddonCommand :: Maybe String -> IO (Maybe Command)