title: Error occurred while installing debugger (1.6.8), and Bundler cannot continue. Make sure that `gem install debugger -v '1.6.8'`
body: <p>There seems to be a recursion effect when installing debugger by <code>gem install debugger -v '1.6.8'</code> it says it is successful installing, but the message reappears when i do <code>bundle install</code> or <code>bundle update</code></p>
  
  <pre><code>|20:15:37| ~ gem install debugger -v '1.6.8'
  Building native extensions.  This could take a while...
  Successfully installed debugger-1.6.8
  Parsing documentation for debugger-1.6.8
  unable to convert "\xCF" from ASCII-8BIT to UTF-8 for lib/ruby_debug.bundle, skipping
  1 gem installed
  |20:15:55| ~ bundle install
  Fetching gem metadata from https://rubygems.org/.......
  Fetching additional metadata from https://rubygems.org/..
  Resolving dependencies......
  Using rake 10.3.2
  Using Ascii85 1.0.2
  Using i18n 0.6.9
  </code></pre>
  
  <p>...</p>
  
  <pre><code>Using coffee-script 2.2.0
  Using coffee-rails 3.2.2
  Using colored 1.2
  Using commonjs 0.2.7
  Using coolline 0.4.4
  Using debugger-ruby_core_source 1.3.5
  
  Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
  
      /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
  checking for rb_method_entry_t.called_id in method.h... no
  checking for rb_control_frame_t.method_id in method.h... no
  checking for rb_method_entry_t.called_id in method.h... no
  checking for rb_control_frame_t.method_id in method.h... no
  checking for rb_method_entry_t.called_id in method.h... yes
  checking for vm_core.h... yes
  checking for iseq.h... no
  Makefile creation failed
  *************************************************************
  
    NOTE: If your headers were not found, try passing
          --with-ruby-include=PATH_TO_HEADERS
  
  *************************************************************
  
  *** extconf.rb failed ***
  Could not create Makefile due to some reason, probably lack of necessary
  libraries and/or headers.  Check the mkmf.log file for more details.  You may
  need configuration options.
  
  Provided configuration options:
      --with-opt-dir
      --without-opt-dir
      --with-opt-include
      --without-opt-include=${opt-dir}/include
      --with-opt-lib
      --without-opt-lib=${opt-dir}/lib
      --with-make-prog
      --without-make-prog
      --srcdir=.
      --curdir
      --ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
      --with-ruby-dir
      --without-ruby-dir
      --with-ruby-include
      --without-ruby-include=${ruby-dir}/include
      --with-ruby-lib
      --without-ruby-lib=${ruby-dir}/
  
  extconf failed, exit code 1
  
  Gem files will remain installed in /var/folders/mp/tl8cpc_j0vd504t3npnqxzl00000gn/T/bundler20140630-67837-rxj9rk/debugger-1.6.8/gems/debugger-1.6.8 for inspection.
  Results logged to /var/folders/mp/tl8cpc_j0vd504t3npnqxzl00000gn/T/bundler20140630-67837-rxj9rk/debugger-1.6.8/extensions/universal-darwin-13/2.0.0/debugger-1.6.8/gem_make.out
  An error occurred while installing debugger (1.6.8), and Bundler cannot continue.
  Make sure that `gem install debugger -v '1.6.8'` succeeds before bundling.
  |20:17:56| ~
  </code></pre>
  
  <p>I have tried <code>bundle update debugger-ruby_core_source</code> and  <code>rm Gemfile.lock</code> then <code>bundle install</code></p>