Apply codespell -w throughout

Backend/External.hs

@@ -158,7 +158,7 @@ sendMessage p m = liftIO $ do
   where
 	line = unwords $ Proto.formatMessage m
 
-{- A response handler can yeild a result, or it can request that another
+{- A response handler can yield a result, or it can request that another
  - message be consumed from the external. -}
 data ResponseHandlerResult a
 	= Result a
@@ -170,7 +170,7 @@ result :: a -> Maybe (Annex (ResponseHandlerResult a))
 result = Just . return . Result
 
 {- Waits for a message from the external backend, and passes it to the
- - apppropriate handler. 
+ - appropriate handler. 
  -
  - If the handler returns Nothing, this is a protocol error.
  -}

Backend/Hash.hs

@@ -281,7 +281,7 @@ md5Hasher = mkHasher md5 md5_context
 descChecksum :: String
 descChecksum = "checksum"
 
-{- A varient of the SHA256E backend, for testing that needs special keys
+{- A variant of the SHA256E backend, for testing that needs special keys
  - that cannot collide with legitimate keys in the repository.
  -
  - This is accomplished by appending a special extension to the key,