Log Message:
[Changes for 0.50 - Nov 10, 2004]

* Workaround fsfs/win32 txn_commit bug in close_edit of mirror editor.
  [Autrijus]

* Use iter pool for node_history tracing.

* Add trailing /... for vcp source if not exist.

* Use the same auth baton for all ra sessions.

* Hold another reference to merge back editor in addition to
  cached_ra, because the callback in merge_back_editor might create
  another ra session.

* Ignore signals before calling close_edit, instead of in commit callback.