[in tools/server-side/svnpubsub]

Make the 'hook' config knob optional.

* svnwcsub.py
  (ReloadableConfig.get_optional_value): New instance method.
  (BigDoEverythingClasss.__init__): Use it for 'hook'.

* svnwcsub.conf.example
  (DEFAULT.hook): Comment it out.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1432790 13f79535-47bb-0310-9956-ffa450edef68