Support svn_client_diff4().
Support svn_client_diff4().

* subversion/bindings/swig/ruby/svn/client.rb
  (Svn::Client::Context#diff): Use Svn::Client.diff4 instead
  of Svn::Client.diff3.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@864398 13f79535-47bb-0310-9956-ffa450edef68

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