On the thunder branch:
Implement the new svn_fs__thunder_t API and provide a test for it. 

* subversion/libsvn_fs_util/thunder.c
  (): New file.

* subversion/tests/libsvn_fs/fs-test.c
  (basic_thunder_interface): New test. 
  (test_func): Register the new test.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/thunder@1586481 13f79535-47bb-0310-9956-ffa450edef68