Please refer this ticket for details.
  This change also introduces the following changes.
  * Remove RGENGC_AGE2_PROMOTION and introduce object age (0 to 3).
    Age can be count with FL_PROMOTE0 and FL_PROMOTE1 flags in
    RBasic::flags (2 bit). Age == 3 objects become old objects.
  * WB_PROTECTED flag in RBasic to WB_UNPROTECTED bitmap.
  * LONG_LIVED bitmap to represent living objects while minor GCs
    It specifies (1) Old objects and (2) remembered shady objects.
  * Introduce rb_objspace_t::marked_objects which counts marked
    objects in current marking phase. marking count is needed to
    introduce incremental marking.
  * rename mark related function and sweep related function to
    gc_(marks|sweep)_(start|finish|step|rest|continue).
  * rename rgengc_report() to gc_report().
  * Add obj_info() function to get cstr of object details.
  * Add MEASURE_LINE() macro to measure execution time of specific line.
  * and many small fixes.
* include/ruby/ruby.h: add flag USE_RINCGC.
  Now USE_RINCGC can be set only with USE_RGENGC.
* include/ruby/ruby.h: introduce FL_PROMOTED0 and add FL_PROMOTED1
  to count object age.
* include/ruby/ruby.h: rewrite write barriers for incremental marking.
* debug.c: catch up flag name changes.
* internal.h: add rb_gc_writebarrier_remember() instead of
  rb_gc_writebarrier_remember_promoted().
* array.c (ary_memcpy0): use rb_gc_writebarrier_remember().
* array.c (rb_ary_modify): ditto.
* hash.c (rb_hash_keys): ditto.
* hash.c (rb_hash_values): ditto.
* object.c (init_copy): use rb_copy_wb_protected_attribute() because
  FL_WB_PROTECTED is moved from RBasic::flags.
* test/objspace/test_objspace.rb: catch up ObjectSpace.dump() changes.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47444 b2dd03c8-39d4-4d8f-98ff-823fe69b080e