Ruby

• vm_trace.c: add two methods:
  (1) TracePoint#return_value which returns return
  value on the :return and :c_return event.
  (2) TracePoint#raised_exception which returns raised exception
  value on the :raise event.
  Eeach methods raise RuntimeError if it is called at unsupported
  event.
  Please review and give us feedback until next preview
  release (Dec/2012) of Ruby 2.0.0.
• insns.def, vm.c, vm_eval.c, vm_insnhelper.c, eval.c, thread.c:
  ditto.
• vm_trace.c, vm_core.h: move definition of rb_trace_arg_t from
  vm_trace.c to vm_core.h.
  Caller fills rb_trace_arg_t and pass the pointer of this variable.
• test/ruby/test_settracefunc.rb: fix tests to test this change.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37752 b2dd03c8-39d4-4d8f-98ff-823fe69b080e