* gc.c: support RGENGC. [ruby-trunk - Feature #8339]
  See this ticet about RGENGC.
* gc.c: Add several flags:
* RGENGC_DEBUG: if >0, then prints debug information.
* RGENGC_CHECK_MODE: if >0, add assertions.
* RGENGC_PROFILE: if >0, add profiling features.
  check GC.stat and GC::Profiler.
* include/ruby/ruby.h: disable RGENGC by default (USE_RGENGC == 0).
* array.c: add write barriers for T_ARRAY and generate sunny objects.
* include/ruby/ruby.h (RARRAY_PTR_USE): added. Use this macro if
  you want to access raw pointers. If you modify the contents which
  pointer pointed, then you need to care write barrier.
* bignum.c, marshal.c, random.c: generate T_BIGNUM sunny objects.
* complex.c, include/ruby/ruby.h: add write barriers for T_COMPLEX
  and generate sunny objects.
* rational.c (nurat_s_new_internal), include/ruby/ruby.h: add write
  barriers for T_RATIONAL and generate sunny objects.
* internal.h: add write barriers for RBasic::klass.
* numeric.c (rb_float_new_in_heap): generate sunny T_FLOAT objects.
* object.c (rb_class_allocate_instance), range.c:
  generate sunny T_OBJECT objects.
* string.c: add write barriers for T_STRING and generate sunny objects.
* variable.c: add write barriers for ivars.
* vm_insnhelper.c (vm_setivar): ditto.
* include/ruby/ruby.h, debug.c: use two flags
  FL_WB_PROTECTED and FL_OLDGEN.
* node.h (NODE_FL_CREF_PUSHED_BY_EVAL, NODE_FL_CREF_OMOD_SHARED):
  move flag bits.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40703 b2dd03c8-39d4-4d8f-98ff-823fe69b080e