* vm_core.h (rb_thread_t): remove rb_thread_t::event_hooks.
* vm_trace.c: all hooks are connected to vm->event_hooks and
add rb_event_hook_t::filter::th to filter invoke thread.
It will simplify invoking hooks code.
* thread.c (thread_start_func_2): clear thread specific trace_func.
* test/ruby/test_settracefunc.rb: add a test for Thread#add_trace_func.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60776 b2dd03c8-39d4-4d8f-98ff-823fe69b080e