Give entries-dump a new mode where it provides a python structure of the entire
subtree's entry data with just a single sqlite transaction.

This adds a new --tree-dump option which dumps everything our python code
wants, but in just a single call to this tool.

* subversion/tests/cmdline/entries-dump.c
  (includes): Add lock.h.
  (entries_dump): Accept a related access baton. Use svn__apr_ to avoid
    ugly casts.
  (directory_walk_baton): Add baton, to allow reusing this struct.

  (tree_dump_dir,
   tree_dump_txn,
   tree_dump): New functions.

  (main): Document and support --tree-dump. Update caller.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1436958 13f79535-47bb-0310-9956-ffa450edef68