Ruby » Ruby master

• thread.c (rb_mutex_owned_p): new method that return current
  thread have the target mutex or not. [Feature #7505] [ruby-dev:46697]
• test/ruby/test_thread.rb (test_mutex_owned, test_mutex_owned2):
  test for the above.
• NEWS: new for the above.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38188 b2dd03c8-39d4-4d8f-98ff-823fe69b080e