libxml2: /opt/local/lib/libz.dylib does not exist

[brett@…]

--->  Fetching libxml2
--->  Attempting to fetch libxml2-2.7.8.tar.gz from http://ykf.ca.distfiles.macports.org/MacPorts/mpdistfiles/libxml2
--->  Verifying checksum(s) for libxml2
--->  Extracting libxml2
--->  Configuring libxml2
Error: The file /opt/local/lib/libz.dylib does not exist, though it was
Error: expected to have been provided by one of libxml2's dependencies. Try
Error: rebuilding the port that should have provided that file by running
Error: 
Error:     sudo port -n upgrade --force <portname>
Error: 
Error: Target org.macports.configure returned: missing required file
Log for libxml2 is at: /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_ports_textproc_libxml2/main.log
Error: Unable to upgrade port: 1
Error: Unable to execute port: upgrade xorg-libXaw failed
To report a bug, see <http://guide.macports.org/#project.tickets>

[brett@…]

Full text from start to finish of the port failure.

[brett@…]

fixed by forcing upgrade to zlib

please close this bug report

thanks for everything you do!!!