Revert part of r1509137: Remove extended constructors for spillbuf reader
and the spillbuf stream wrapper.

* subversion/include/private/svn_subr_private.h
  (svn_spillbuf__reader_create_extended,
   svn_stream__from_spillbuf_extended): Removed.
* subversion/libsvn_subr/spillbuf.c
  (svn_spillbuf__reader_create_extended,
   svn_stream__from_spillbuf,
   svn_stream__from_spillbuf_extended): Removed.
  (stream_from_reader): Renamed to svn_stream__from_spillbuf.
* subversion/tests/libsvn_subr/spillbuf-test.c
  (test_spillbuf_reader): Renamed from test_spillbuf__reader.
  (test_spillbuf_stream): Renamed from test_spillbuf__stream.
  (test_spillbuf_reader_spill_all,
   test_spillbuf_stream_spill_all): Removed.
  (test_funcs): Deleted obsolete tests.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1509577 13f79535-47bb-0310-9956-ffa450edef68