Various improvements to the "clean checkout" optimization applicability check. See http://svn.haxx.se/dev/archive-2011-05/0479.shtml for details
Various improvements to the "clean checkout" optimization applicability check.
See http://svn.haxx.se/dev/archive-2011-05/0479.shtml for details

* subversion/libsvn_client/update.c
  (is_empty_wc): make return parameter the first in the list;
   improve commentary; return "optimization not applicable" 
   upon any unexpected problem
  (update_internal): adapt caller

Suggested by: danielsh

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1104306 13f79535-47bb-0310-9956-ffa450edef68

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