* include/ruby/thread.h: new header file for thread stuff.
* thread.c (rb_thread_call_without_gvl): export.  [Feature#4328]
  returns void* instead of VALUE.  [Feature #5543]
* thread.c (rb_thread_blocking_region): deprecate.  [ruby-core:46295]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36355 b2dd03c8-39d4-4d8f-98ff-823fe69b080e