Add a regression test for the SEGV fixed by r1482327.

* subversion/tests/cmdline/upgrade_tests.py
  (changelist_upgrade_1_6): New.
  (test_funcs): add new test.

* subversion/tests/cmdline/upgrade_tests_data/changelist_upgrade_1_6.tar.bz2:
  New file.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1482338 13f79535-47bb-0310-9956-ffa450edef68