added a java_field method for use in the jrubyc command. also added a runtime stub.
Merge pull request #1765 from jkutner/add_fields_to_java_gen

added a java_field method for use in the jrubyc command.
get ant back for tests
Merge branch 'jruby-1_7' of jruby.org:jruby into jruby-1_7