[PATCH] issue #3242: fix another occurence

Hi,
the fixes for issue 3242 ("Subversion demands unnecessary access
to parent directories of operations") currently in trunk do not address
scenario gicen below.

[[[
Fix another scenario related to issue #3242:

- user has no access in repo root, only in /project
- someone else renames some file below /project and commits
- user tries to update his working copy of /project
  (that still has the old name)
- update deletes the old name and then fails with
  "access to 'http://host/repo-root' forbidden"

* subversion/libsvn_client/update.c
  (file_fetcher): When opening an auxiliary session, don't open it at the
  repository root (where the user might not have read permission), but
  at the dirname of the file to fetch.
]]]

The first attached patch amends authz_tests.py with a test for the
above scenario,
the second patch is the actual fix.

Cheers, Roderich