gc.c: split GC_END event into GC_END_MARK and GC_END_SWEEP

* include/ruby/ruby.h: remove INTERNAL_EVENT_GC_END and replace with
  two new events: GC_END_MARK and GC_END_SWEEP
* gc.c (gc_after_sweep): emit GC_END_SWEEP after lazy sweep is done
* gc.c (gc_marks_body): emit GC_END_MARK at end of minor/major mark
* ext/-test-/tracepoint/tracepoint.c (struct tracepoint_track): tests
  for new events.
* test/-ext-/tracepoint/test_tracepoint.rb (class TestTracepointObj):
  ditto.
* NEWS: remove ObjectSpace.after_gc_*_hook. These are only a sample,
  and will be removed before ruby 2.1.
* ext/objspace/gc_hook.c: remove ObjectSpace.after_gc_end_hook=

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43997 b2dd03c8-39d4-4d8f-98ff-823fe69b080e