Ruby

• vm_core.h: remove VM_FRAME_MAGIC_FINISH (finish frame type).
  Before this commit:
  finish frame' was place holder which indicates that VM loop needs to return function. If a C method calls a Ruby methods (a method written by Ruby), then VM loop will be (re-)invoked. When the Ruby method returns, then also VM loop should be escaped. finish frame' has only
  one instruction finish', which returns VM loop function. VM loop function executes finish' instruction, then VM loop
  function returns itself.
  With such mechanism, leave' instruction (which returns one frame from current scope) doesn't need to check that this leave'
  should also return from VM loop function.
  Strictly, one branch can be removed from leave' instructon. Consideration: However, pushing the finish frame' needs costs because
  it needs several memory accesses. The number of pushing
  finish frame' is greater than I had assumed. Of course, pushing finish frame' consumes additional control frame.
  Moreover, recent processors has good branch prediction,
  with which we can ignore such trivial checking.
  After this commit:
  Finally, I decide to remove finish frame' and finish'
  instruction. Some parts of VM depend on finish frame', so the new frame flag VM_FRAME_FLAG_FINISH is introduced. If this frame should escape from VM function loop, then the result of VM_FRAME_TYPE_FINISH_P(cfp) is true. leave' instruction checks this flag every time.
  I measured performance on it. However on my environments,
  it improves some benchmarks and slows some benchmarks down.
  Maybe it is because of C compiler optimization parameters.
  I'll re-visit here if this cause problems.
• insns.def (leave, finish): remove finish instruction.
• vm.c, vm_eval.c, vm_exec.c, vm_backtrace.c, vm_dump.c:
  apply above changes.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36099 b2dd03c8-39d4-4d8f-98ff-823fe69b080e