write bundler version
Fix bundler git gemspec bug.

Bundler 1.3.0.pre.8 broke backwards compatibility with gemspecs.
6548e31e8ad061403d65505d7d2e17c489b262cc changes how gemspecs are being
generated which is causing problems with git gemspecs that are not self
contained. See https://gist.github.com/hone/5043f02bea633fd1a844 for the
differences in the gemspec.
v57 bump
only clear the cache if the bundle contains git gems
scope bundle cache removal to git gems
update changelog
fix bundle install for ruby 1.8.7

Bundler gets removed from the `$LOAD_PATH` for some reason in ruby 1.8.7.
This means we shouldn't try to require something from bundler here.

> Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native
> extension.
>
>        /home/hone/.rvm/rubies/ruby-1.8.7-p371/bin/ruby extconf.rb
> /home/hone/.rvm/rubies/ruby-1.8.7-p371/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in
> `gem_original_require': no such file to load -- bundler/psyched_yaml
> (LoadError)
>         from
> /home/hone/.rvm/rubies/ruby-1.8.7-p371/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in
> `require'
>         from
> /home/hone/Projects/heroku_work/heroku-buildpack-ruby/vendor/syck_hack.rb:15
rework to use psyched_yaml by adding Bundler to $LOAD_PATH
don't need syck hack for bundle version
bump v58
update changelog
Merge remote-tracking branch 'upstream/master'