Revision 1818584

Fix a refcounting / cleanup race in svn_object_pool causing crashes when
exiting svnserve while using the --config-file option.

This patch has been outstandig for a while:
    URL: https://lists.apache.org/thread.html/41ca5579bf7add3cb751234ea039fda531c1d22ffbed8cb2ec699e42@%3Cdev.subversion.apache.org%3E
    From: stefan2
    To: dev@
    Subject: Re: heap-use-after-free in object_ref_cleanup
    Date: 2017-05-28 16:46

* subversion/libsvn_subr/object_pool.c
  (add_object_ref):  If items of the container are being hold by parent pools
                     of the container pool, ref counting updates would come
                     too late if run during pool cleanup.  Instead, run them
                     in pre-cleanup.