variable.c: cleanup waitq upon thread death
* variable.c (autoload_reset): use idempotent list_del_init
(autoload_sleep): moved code from rb_autoload_load
(autoload_sleep_done): cleanup for use with rb_ensure
(rb_autoload_load): ensure list delete happens in case the
thread dies during sleep
* test/ruby/bug-13526.rb: new script for separate execution
* test/ruby/test_autoload.rb (test_bug_13526): new test
[ruby-core:81016] [Bug #13526]
* properties.
merge revision(s) 58587,58588: [Backport #13526]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@59219 b2dd03c8-39d4-4d8f-98ff-823fe69b080e