remote-testgit: implement the "done" feature manually

People who want to write their own remote-helper will find it more
useful to see clearly how they are supposed to advertise and implement
the "done" feature themselves.

Right now we are relying on fast-export to do that by using the
--use-done-feature argument. However, people writing their own
remote-helper would probably not have such an option, as they would
probably be writing the fast-export functionality themselves.

It should now be clearer to them.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-remote-testgit

@@ -61,8 +61,10 @@ do
 			echo "feature import-marks=$gitmarks"
 			echo "feature export-marks=$gitmarks"
 		fi
-		git fast-export --use-done-feature "${testgitmarks_args[@]}" $refs |
+		echo "feature done"
+		git fast-export "${testgitmarks_args[@]}" $refs |
 		sed -e "s#refs/heads/#${prefix}/heads/#g"
+		echo "done"
 		;;
 	export)
 		before=$(git for-each-ref --format='%(refname) %(objectname)')