Return in a proc given to define_method does not return

[enebo]

Originally from http://jira.codehaus.org/browse/JRUBY-6122

  class DefineMethod
    lamb = proc { return :good }
    define_method :foo, lamb

    def outer
      val = :bad

      # This is tricky, but works. If lamb properly returns, then the
      # return value will go into val before we run the ensure.
      #
      # If lamb's return keeps unwinding incorrectly, val will still
      # have it's old value.
      #
      # We can therefore use val to figure out what happened.
      begin
        val = foo()
      ensure
        if val != :good
          return :bad
        end
      end

      return val
    end
  end