Add an LZ4 compressed stream.

* subversion/include/private/svn_io_private.h
  (svn_stream__lz4_compressed): New; stream constructor prototype.
* subversion/libsvn_subr/stream.c
  (zbaton): Unrelated change: make substrem an svn_stream_t*.
  (lz4_baton,
   read_handler_lz4,
   ensure_write_buffer_lz4,
   write_handler_lz4,
   close_handler_lz4): New LZ4 stream helpers.
  (svn_stream__lz4_compressed): Implement the stream constructor.

* subversion/tests/libsvn_subr/stream-test.c
  (do_test_stream_compressed): Renamed and refactored from
   test_stream_compressed().
  (test_stream_compressed,
   test_stream_compressed_lz4): Test drivers for the above.
  (test_funcs): Register the new test.

* build.conf
  (slz4): New tool, simulates lz4/unlz4.
  (tools/lz4/slz4.c): Implement the lz4/unlz4 simulator.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/better-pristines@1931688 13f79535-47bb-0310-9956-ffa450edef68