Remove the no longer necessary hack that selectively allowed adding working
copy roots when the current directory was that working copy root. Integrate
this with the new wcroot check code to simplify the result.

Also properly handle svn add --force on symlinks (regression in r1395027)

* subversion/libsvn_client/add.c
  (svn_client_add4): Remove a documented 'hack' that is no longer necessary
    since we now always allow adding an already versioned directory.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1395082 13f79535-47bb-0310-9956-ffa450edef68