* iseq.c: before this patch, RubyVM::InstructionSequence.of(src) (ISeq in
  short) returns different ISeq (wrapper) objects point to one ISeq internal
  object. This patch changes this behavior to cache created ISeq (wrapper)
  objects and return same ISeq object for an internal ISeq object.

* iseq.h (ISEQ_EXECUTABLE_P): introduced to check executable ISeq objects.

* iseq.h (ISEQ_COMPILE_DATA_ALLOC): reordr setting flag line to avoid
  ISEQ_USE_COMPILE_DATA but compiled_data == NULL case.

* vm_core.h (rb_iseq_t): introduce `rb_iseq_t::wrapper` and
  `rb_iseq_t::aux::exec`.  Move `rb_iseq_t::local_hooks` to
  `rb_iseq_t::aux::exec::local_hooks`.

* test/ruby/test_iseq.rb: add ISeq.of() tests.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66246 b2dd03c8-39d4-4d8f-98ff-823fe69b080e