Fix issue #4139 'Subversion cannot perform merge if there's a file with
the same name as directory'.

* subversion/svn/merge-cmd.c
  (svn_cl__merge): If the basename of the source is the same as the
   basename of the current working directory, then assume the cwd is the
   target.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1431114 13f79535-47bb-0310-9956-ffa450edef68