with ra_neon, Unlocking a file succeeds in client side, though pre-unlock hook exits with
non-zero return code.

* subversion/libsvn_ra_neon/lock.c
  (do_unlock): Handle the error by default.
* subversion/tests/cmdline/lock_tests.py
  (block_unlock_if_pre_unlock_hook_fails): Add a test case.

Patch by: Vijayaguru G <vijay{_AT_}collab.net>