Migrate JRuby from 1.6.8 to 1.7.0

In this week, JRuby 1.7.0 final has been released. This release becomes Ruby-1.9-based product. so that we should take care of migrating from 1.6.8 (or former) to 1.7.0 (or later).

1. rename directory from jruby-1.6.8 to jruby-1.7.0
2. rename from jruby-1.6.8/lib/ruby/gems/1.8 to jruby-1.7.0/lib/ruby/gems/shared