vm_insnhelper.c: add comments

	* vm_insnhelper.c (vm_yield_setup_block_args): break a long line and
  add comments.  remove useless code.
	* vm_insnhelper.c (vm_yield_setup_block_args): split single parameter
	  if any keyword arguments exist, and then extract keyword arguments.
	  [ruby-core:55203] [Bug #8463]

	* compile.c (iseq_set_arguments): not a simple single argument if any
	  keyword arguments exist.  [ruby-core:55203] [Bug #8463]

	* vm_insnhelper.c (vm_yield_setup_block_args): partially revert r41019.
	  The code is not useless.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@41262 b2dd03c8-39d4-4d8f-98ff-823fe69b080e