Allow ZLIB_LIBDIR to be set to specify where the output of the zlib build can be found.
Allow ZLIB_LIBDIR to be set to specify where the output of the zlib build
can be found.

* serf.mak: Support zlib with MSVC 2005 builds.

jandre/serf,jandre/serf,jandre/serf,jandre/serf