Hi Joerg,
please make suggestions about the xyz_LIBRARY_PATH MacOS issue that allows libpng.so and libfreetype.so to be found at run-time in /usr/X11/lib (bug 17674).
I agree with Alexandre on this one: it's just an error in your configuration. You can address it by adding /usr/X11/lib to LD_LIBRARY_PATH or DYLD_FALLBACK_LIBRARY_PATH in your ~/.bash_profile or ~/.bashrc if you like, assuming you start wine apps from the command line. If you use some other launcher, the environment needs to be set correctly for that.
Another way of looking at the error is that MacPorts (and fink, I presume) install libraries to a path that's not searched by default. Perhaps this is what you want, and perhaps not, but that's up to you, not up to Wine. --Juan