The problem was that libssl-1.0.0.dylib was linked to the wrong lib in the DMG. Adding +w rights to libssl and libcrypto in /opt/local/lib fixed that. Looking at output from dylibbundler reveals another problem though:
Log: Deploying Qt frameworks found inside: ("./x2goclient.app/Contents/PlugIns/imageformats/libqtiff.dylib")
Log: copied: "/opt/local/lib/libtiff.5.dylib"
Log: to "./x2goclient.app/Contents/Frameworks//libtiff.5.dylib"
ERROR: "install_name_tool: changing install names or rpaths can't be redone for: ./x2goclient.app/Contents/Frameworks//libtiff.5.dylib (for architecture x86_64) because larger updated load commands do not fit (the program must be relinked, and you may need to use -headerpad or -headerpad_max_install_names)
"
ERROR: ""
ERROR: "install_name_tool: changing install names or rpaths can't be redone for: ./x2goclient.app/Contents/Frameworks//libtiff.5.dylib (for architecture x86_64) because larger updated load commands do not fit (the program must be relinked, and you may need to use -headerpad or -headerpad_max_install_names)
"
ERROR: ""
I have added +w to libtiff.5.dylib. Any idea what could be the problem there?