Ruby » Ruby master

merge revision(s) 57255,57256,57257: [Backport #13111]

    forwardable.rb: use defined?

    * lib/forwardable.rb (_delegator_method): use defined? operator
      instead of binding and calling unbound Kernel#respond_to?.  a
      remedy for an performance bottleneck.
    forwardable.rb: use defined?

    * lib/forwardable.rb (_delegator_method): use defined? operator
      instead of binding and calling unbound Kernel#respond_to?.  a
      remedy for an performance bottleneck.
    forwardable.rb: fix branches

    * lib/forwardable.rb (instance_delegate, single_delegate): fix
      inverted branches.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@57913 b2dd03c8-39d4-4d8f-98ff-823fe69b080e