JRuby native support for Racc

This set of commits does the following:

* Port of ext/racc/cparse.c to Java/JRuby.
* Logic to build ext/racc-cparse.jar.
* lib/racc/parser.rb changes to load the JRuby ext.
* Partial logic to build the -java gem with the jar inside.

Bad news: I could not quite get the gem to build correctly. I don't get how rack-compiler and the rake-extensiontask stuff do their magic.

Good news: all tests pass, and `rake test` works.