* NEWS: Add ObjectSpace.after_gc_{start,end}_hook=
* ext/objspace/objspace_dump.c: [DOC] catch up dump/dump_all to r43679

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43847 b2dd03c8-39d4-4d8f-98ff-823fe69b080e