* iseq.c (iseqw_each_child): add RubyVM::InstructionSequence#each_child
method for tools which want to manipulate ISeq.
* test/ruby/test_iseq.rb: add a test for this method.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61425 b2dd03c8-39d4-4d8f-98ff-823fe69b080e