Rake compiler doesn't actually work. In MRI, there's an `install_so` target in the makefile, which actually puts the shared object in some odd place in your load path (at least it does if you run `make install` outside of rubygems). On top of that, there's some oddness in the naming of the shared object, because `RbConfig::CONFIG["DLEXT"] == "jar"` on JRuby. So when you compile on JRuby, you get `dep_gecode.jar` which is actually a ELF/Mach-O/whatever shared object/bundle. That's kind of ugly (it works though), but I'm not sure how to reimplement the logic to figure out what the correct extension name should be.