Have svnmerge.py check for _svn directories to see if a directory is a working copy.
Have svnmerge.py check for _svn directories to see if a directory is a
working copy.

* contrib/client-side/svnmerge.py
  (is_wc):
    If _svn exists and is a directory, then return True.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@858692 13f79535-47bb-0310-9956-ffa450edef68

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