* debug_counter.h: add comments for each counters.

* debug_counter.h: add some counters (see added comments for details).
  * obj_newobj
  * obj_newobj_slowpath
  * obj_newobj_wb_unprotected
  * obj_hash_empty
  * obj_hash_under4
  * obj_hash_ge4
  * obj_hash_ge8
  * heap_xmalloc
  * heap_xrealloc
  * heap_xfree

* gc.c: add some debug counters (see the above list).

* debug_counter.c (rb_debug_counter_show_results): accept
  a header message.

* signal.c (ruby_default_signal): show debug counter results
  and malloc info (rb_malloc_info_show_results()) before
  SIGNAL exit.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64841 b2dd03c8-39d4-4d8f-98ff-823fe69b080e