[Bug #12628]

  This patch introduce many changes.

  * Introduce concept of "Block Handler (BH)" to represent
    passed blocks.

  * move rb_control_frame_t::flag to ep[0] (as a special local
    variable). This flags represents not only frame type, but also
    env flags such as escaped.

  * rename `rb_block_t` to `struct rb_block`.

  * Make Proc, Binding and RubyVM::Env objects wb-protected.

  Check [Bug #12628] for more details.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55766 b2dd03c8-39d4-4d8f-98ff-823fe69b080e