bsr_jsr_ret branch

[Andrew Whitworth]

I've been working on the bsr_jsr_ret branch, which is supposed to be
removing those three opcodes. I'm done all the major work in it and am
ready to merge it into trunk. However, I just did a spectest run for
Rakudo in that branch, and there were some failures. I don't know how
many of those failures are new to the branch, or how many are the
result of other changes made to Parrot recently.

I'd like a little bit of feedback on that branch, and would like to
get it merged in to trunk (unless it's causing all sorts of b0rked
failures) this weekend.

--Andrew Whitworth