Add regression test for the ZLib decompression problem identified in
ZLib 1.2.8 with assembly optimizations enabled.

This should make it easier for packagers to find out if they need to
fix their installation.

* subversion/tests/libsvn_subr/checksum-test.c
  (includes): Add zlib.h and svn_io.h.
  (zlib_expansion_test): New function.
  (test_funcs): Add zlib_expansion_test.

* subversion/tests/libsvn_subr/zlib.deflated
  Add the compressed version of an old Subversion CHANGES file that showcased
  the original compression problem.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1537193 13f79535-47bb-0310-9956-ffa450edef68