Remove the special obstructed-add handler from svn's conflict callback.
It doesn't work with the current libsvn_wc implementation. The "mf" and
"tf" options it offers error out with "tree conflicts can only be resolved
to working state".

The only remaining way to trigger this handler was by merging an addition
of a file on top of a directory (or vice versa).
This case is now handled by the generic tree conflict code, which doesn't
offer the unsupported options:
     > local dir obstruction, incoming file add upon merge
  Select: (r) mark resolved, (p) postpone, (q) quit resolution, (h) help:

* subversion/svn/conflict-callbacks.c
  (obstructed_add_options, handle_obstructed_add): Remove.
  (conflict_func_interactive): Stop calling handle_obstructed_add(). 


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1620332 13f79535-47bb-0310-9956-ffa450edef68