Remove more compatability code for pre-1.3.x APR.

* subversion/include/private/svn_atomic.h
  (svn_atomic_t, svn_atomic_read, svn_atomic_set, svn_atomic_int,
   svn_atomic_dec, svn_atomic_cas): Assume the 32 bit versions of APR atomic
     functions are available.

* subversion/libsvn_ra_serf/commit.c
  (create_put_body): Always use apr_file_buffer_set().

* subversion/libsvn_ra_serf/update.c
  (body_done_fn): Always use apr_file_buffer_set().

* subversion/libsvn_subr/hash.c
  (svn_hash__clear): Remove the now unused function.

* subversion/libsvn_subr/io.c
  (svn_io_file_aligned_seek): Assume apr_file_buffer_set() is always available.

* subversion/libsvn_subr/utf.c
  (atomic_swap): Assume apr_atomic_xchangptr() is always available.

* subversion/svnserve/svnserve.c
  (HAVE_THREADPOOLS): Remove, we always have thread pools if we have threads.
  (THREAD_ERROR_MSG): Remove
  (serve_thread): Remove implementation that doesn't know about thread pools.
  (sub_main): Remove now unused tattr and tid local variables, assume we have
    thread pools if we have threads.
  (main): Assume we have thread pools if we have threads.

* subversion/tests/libsvn_subr/io-test.c
  (aligned_seek): Remove compat code for old versions of APR that were limited
    to 4k blocks.

* tools/server-side/fsfs-stats.c
  (get_content): Assume we can always use large read buffers.



git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1572303 13f79535-47bb-0310-9956-ffa450edef68