Fix install on JRuby

As part of a Java-based build system, I'd like to run Sproutcore under JRuby. These patches allow it to build and run under JRuby 1.7.12; older versions may or may not work. The proxy functionality in the server would need to be fixed not to depend on thin for that to work.

Note that with these patches, Sproutcore will still have to be built from source under JRuby, as the gemspec is run at build time, not install time. To fix this, a workaround like [this](http://en.wikibooks.org/w/index.php?title=Ruby_Programming/RubyGems&oldid=1883974#How_to_install_different_versions_of_gems_depending_on_which_version_of_ruby_the_installee_is_using) would have to be used, which uses an extension definition to choose which gems to install at install