Bootstrapping rspec tests

Added hook in the :test task for running rspec tests from Build.
This works prety nicely, except that JRuby does not know about static
methods in Java 8 interfaces. For now I added an "helper" static class
to get access to Seq#nil(). Possible work-around would be to see if I
can create a dispatch module onto which hooks to the static methods in
the interface can be added. I must first look at what kind of bytecode
are generated for interface static methods.
More rspec tests for Seq