git-svn: fix following renamed paths when tracking a single path

git-svn: fix following renamed paths when tracking a single path

When using git-svn to follow only a single (empty) path per
svn-remote (i.e. not using --stdlayout), following the history
of a renamed path was broken in
c586879cdfa4f8181a14e953a9152a4639eef333.

This reverts the regression for the single (emtpy) path per
svn-remote case.

To avoid breaking the tests in a committed revision, this is an
addendum to a patch originally submitted by

  Santhosh Kumar Mani <santhoshmani@gmail.com>:
  > git-svn: add test for renamed directory fetch
  >
  > This test tries to fetch a directory which had renames in the
  > history from a SVN repository.

  [ew: unneccesary dependency on the starting an HTTP server
   removed from Santhosh's original test.]

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>