invokespecial on abstract method

[Erik Poupaert]

> Our tests so far have shown that the performance impact of the 
> BC-ABI/-findirect-dispatch is somewhere between zero and "minimal". See: 
> http://flint.cs.yale.edu/flint/publications/bincomp.html

Looks like they did quite a bit of homework for their paper. Given the amount of
thinking that went into this approach, I look forward to trying this out.