Use http-conduit for url downloads by default, annex.web-options enables curl

* For url downloads, git-annex now defaults to using a http library,
  rather than wget or curl. But, if annex.web-options is set, it will
  use curl. To use the .netrc file, run:
    git config annex.web-options --netrc
* git-annex no longer uses wget (and wget is no longer shipped with
  git-annex builds).

Note that curl is always run in silent mode, since the new API for
download has a MeterUpdate and doesn't make way for curl progress
output. It might be worth writing a parser for curl's progress output
to update the meter when using it, but I didn't bother with this edge
case for now.

This commit was supported by the NSF-funded DataLad project.

Command/ImportFeed.hs

@@ -33,6 +33,7 @@ import Logs.Web
 import Logs.File
 import qualified Utility.Format
 import Utility.Tmp
+import Utility.Metered
 import Command.AddUrl (addUrlFile, downloadRemoteFile, parseDownloadOptions, DownloadOptions(..))
 import Annex.UUID
 import Backend.URL (fromUrl)
@@ -148,15 +149,13 @@ findDownloads u = go =<< downloadFeed u
 downloadFeed :: URLString -> Annex (Maybe Feed)
 downloadFeed url
 	| Url.parseURIRelaxed url == Nothing = giveup "invalid feed url"
-	| otherwise = do
-		showOutput
-		Url.withUrlOptions $ \uo ->
-			liftIO $ withTmpFile "feed" $ \f h -> do
-				hClose h
-				ifM (Url.download url f uo)
-					( parseFeedString <$> readFileStrict f
-					, return Nothing
-					)
+	| otherwise = Url.withUrlOptions $ \uo ->
+		liftIO $ withTmpFile "feed" $ \f h -> do
+			hClose h
+			ifM (Url.download nullMeterUpdate url f uo)
+				( parseFeedString <$> readFileStrict f
+				, return Nothing
+				)
 
 performDownload :: ImportFeedOptions -> Cache -> ToDownload -> Annex Bool
 performDownload opts cache todownload = case location todownload of