Ruby » Ruby master

IO#close: do not enqueue redundant interrupts

Enqueuing multiple errors for one event causes spurious errors
down the line, as reported by Nikolay Vashchenko in
https://bugs.ruby-lang.org/issues/13632

• thread.c (rb_notify_fd_close): do not enqueue multiple interrupts
  [ruby-core:81581] [Bug #13632]
• test/ruby/test_io.rb (test_single_exception_on_close):
  new test based on script from Nikolay

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59020 b2dd03c8-39d4-4d8f-98ff-823fe69b080e