Send a git-annex user-agent when downloading urls.

Overridable with --user-agent option.

Not yet done for S3 or WebDAV due to limitations of libraries used --
nether allows a user-agent header to be specified.

This commit sponsored by Michael Zehrer.

Command/ImportFeed.hs

@@ -17,7 +17,7 @@ import Data.Time.Clock
 import Common.Annex
 import qualified Annex
 import Command
-import qualified Utility.Url as Url
+import qualified Annex.Url as Url
 import Logs.Web
 import qualified Option
 import qualified Utility.Format
@@ -102,9 +102,10 @@ findEnclosures url = extract <$> downloadFeed url
 downloadFeed :: URLString -> Annex (Maybe Feed)
 downloadFeed url = do
 	showOutput
+	ua <- Url.getUserAgent
 	liftIO $ withTmpFile "feed" $ \f h -> do
 		fileEncoding h
-		ifM (Url.download url [] [] f)
+		ifM (Url.download url [] [] f ua)
 			( liftIO $ parseFeedString <$> hGetContentsStrict h
 			, return Nothing
 			)