Report duplicate tree conflict errors in just one place (follow-up to r38872).
Report duplicate tree conflict errors in just one place (follow-up
to r38872).

* subversion/libsvn_client/merge.c
  (tree_conflict_on_add): Remove redundant error handling.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion