Use client cancellation function to cancel ra operations when present.
Use client cancellation function to cancel ra operations when present.

* subversion/libsvn_client/ra.c
  (cancel_callback): New. Forwards cancellation calls to the
   client-specified cancellation callback.
  (svn_client__open_ra_session_internal): Initialize the RA cancellation
   callback member of svn_ra_callbacks2_t introduced in r22294.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@862369 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion