A quick check of OS X Lion shows:
$ otool -L /usr/X11/lib/libpixman-1.0.dylib /usr/X11/lib/libpixman-1.0.dylib: /usr/X11/lib/libpixman-1.0.dylib (compatibility version 21.0.0, current version 21.2.0) /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 159.1.0)
If your libpixman-1.0 library has something different (i.e.: not version 21.x.x), you may want to re-install X11 from the Lion CD.