Improve the value we provide to delete_entry() in the repos reporter.
Improve the value we provide to delete_entry() in the repos reporter.

This is a general correctness improvement, but also fixes a couple of test
failures in the Ev2 shims.

Current number of Ev2 test failures: 11

* subversion/libsvn_repos/reporter.c
  (update_entry): If we can't find the deleted revision, attempt to find a
    suitable value to provide for delete_entry().

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion