* internal.h: added a declaration of ruby_kill().
* thread.c (ruby_kill): helper function of kill().

* signal.c (rb_f_kill): use ruby_kill() instead of kill().
* signal.c (rb_f_kill): call rb_thread_execute_interrupts()
  to ensure that make SignalException if sent a signal
  to myself. [Bug #7951] [ruby-core:52864]

* vm_core.h (typedef struct rb_thread_struct): added
  th->interrupt_cond.
* thread.c (rb_threadptr_interrupt_common): added to
  initialization of th->interrupt_cond.
* thread.c (thread_create_core): ditto.

* test/ruby/test_signal.rb (TestSignal#test_hup_me): test for
  the above.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39819 b2dd03c8-39d4-4d8f-98ff-823fe69b080e