Web site: clean up the description of future plug-in diff support.
Web site: clean up the description of future plug-in diff support.

* www/index.html
  Remove a spurious syntax description.
  Mention that we already support plug-in diff for text files.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@849196 13f79535-47bb-0310-9956-ffa450edef68

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