bundle install に失敗する

gistfile1.md

% rbenv exec bundle install --path=vendor/bundle                                                                                                              
Fetching source index from http://rubygems.org/
Using rake (10.0.3) 
(中略)
Using debugger-ruby_core_source (1.1.5) 
Installing debugger-linecache (1.1.2) 
Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

        /usr/local/opt/rbenv/versions/1.9.3-p392/bin/ruby extconf.rb 
checking for vm_core.h... no
checking for vm_core.h... no
Makefile creation failed
**************************************************************************
No source for ruby-1.9.3-p392 provided with debugger-ruby_core_source gem.
**************************************************************************
*** 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=/usr/local/opt/rbenv/versions/1.9.3-p392/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}/lib


Gem files will remain installed in /Users/ONDA/rails_project/vendor/bundle/ruby/1.9.1/gems/debugger-linecache-1.1.2 for inspection.
Results logged to /Users/ONDA/rails_project/vendor/bundle/ruby/1.9.1/gems/debugger-linecache-1.1.2/ext/trace_nums/gem_make.out

An error occurred while installing debugger-linecache (1.1.2), and Bundler cannot continue.
Make sure that `gem install debugger-linecache -v '1.1.2'` succeeds before bundling.

% bundle update debugger

を実行したらうまくいった。