On the 'moves-tracking-2' branch: implement node-content constructors.

* subversion/include/private/svn_editor3.h
  (svn_editor3_node_content_t): Add a 'node kind' field.
  (svn_editor3_node_content_create_dir,
   svn_editor3_node_content_create_file,
   svn_editor3_node_content_create_symlink):
    Make these constructors return the new object directly.

* subversion/libsvn_delta/editor3.c
  (svn_editor3_node_content_create_dir,
   svn_editor3_node_content_create_file,
   svn_editor3_node_content_create_symlink): Implement.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/move-tracking-2@1606934 13f79535-47bb-0310-9956-ffa450edef68