I just had a need to decode a piece of Zlib data from out of the

middle of a PDF. So here's a modification to sshzlib.c which enables
it to be compiled into a standalone Zlib decoder if you define
ZLIB_STANDALONE. As an added bonus, it (both standalone and in
PuTTY) also validates the Zlib header, just to make sure someone
hasn't defined a new compression format.

git-svn-id: svn://svn.tartarus.org/sgt/putty@4657 cda61777-01e9-0310-a592-d414129be87e