Original distribution from http://zlib.net/.  Currently, only trivial
changes were made to support build of libstand and to suppress certain
compiler warnings, we upstream our local changes whenever they would
benefit other consumers.

To Update:
  1) Unpack vendor sources into a clean directory.
  2) Import onto the vendor area.
  3) Merge the vendor tree to sys/contrib/zlib, which contains a stripped down
     version of upstream source, resolve any conflicts.
  4) Double check zconf.h, zlib.pc, and Symbol.map to make sure that we
     have the required changes.  Test universe and commit them.

delphij@FreeBSD.org