Fix reversion in display of http 404 errors.

Switch to using http-client for large file downloads caused the reversion;
the code for displaying a 404 response was instead displaying the raw html
document, which is not useful.

This commit was sponsored by Ryan Newton on Patreon.

CHANGELOG

@@ -1,3 +1,9 @@
+git-annex (6.20180720) UNRELEASED; urgency=medium
+
+  * Fix reversion in display of http 404 errors.
+
+ -- Joey Hess <id@joeyh.name>  Tue, 31 Jul 2018 12:14:11 -0400
+
 git-annex (6.20180719) upstream; urgency=medium
 
   * Support working trees set up by git-worktree.

Utility/Url.hs

@@ -362,8 +362,8 @@ download meterupdate url file uo =
 	showhttpexception he = do
 #if MIN_VERSION_http_client(0,5,0)
 		let msg = case he of
-			HttpExceptionRequest _ (StatusCodeException _ msgb) ->
-				B8.toString msgb
+			HttpExceptionRequest _ (StatusCodeException r _) ->
+				B8.toString $ statusMessage $ responseStatus r
 			HttpExceptionRequest _ (InternalException ie) -> 
 				case fromException ie of
 					Nothing -> show ie