Make sure to have a require for `riak/failed_request` at the top. Running `bundle console` within the project gives me this error:

```
$ bundle console
Resolving dependencies...
      Unfortunately, a fatal error has occurred. Please see the Bundler
      troubleshooting documentation at http://bit.ly/bundler-issues. Thanks!
/Users/sean/dev/riak-ruby-client/lib/riak/counter.rb:96:in `<class:Counter>': uninitialized constant Riak::FailedRequest (NameError)
	from /Users/sean/dev/riak-ruby-client/lib/riak/counter.rb:5:in `<module:Riak>'
	from /Users/sean/dev/riak-ruby-client/lib/riak/counter.rb:1:in `<top (required)>'
	from /Users/sean/dev/riak-ruby-client/lib/riak/bucket.rb:4:in `require'
	from /Users/sean/dev/riak-ruby-client/lib/riak/bucket.rb:4:in `<top (required)>'
	from /Users/sean/dev/riak-ruby-client/lib/riak/map_reduce.rb:5:in `require'
	from /Users/sean/dev/riak-ruby-client/lib/riak/map_reduce.rb:5:in `<top (required)>'
	from /Users/sean/dev/riak-ruby-client/lib/riak.rb:4:in `require'
	from /Users/sean/dev/riak-ruby-client/lib/riak.rb:4:in `<top (required)>'
	from /Users/sean/dev/riak-ruby-client/lib/riak/client.rb:4:in `require'
	from /Users/sean/dev/riak-ruby-client/lib/riak/client.rb:4:in `<top (required)>'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/runtime.rb:81:in `require'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/runtime.rb:81:in `rescue in block in require'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/runtime.rb:66:in `block in require'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/runtime.rb:59:in `each'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/runtime.rb:59:in `require'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler.rb:132:in `require'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/cli.rb:610:in `console'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/vendor/thor/task.rb:27:in `run'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/vendor/thor/invocation.rb:120:in `invoke_task'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/vendor/thor.rb:344:in `dispatch'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/vendor/thor/base.rb:434:in `start'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/bin/bundle:20:in `block in <top (required)>'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/lib/bundler/friendly_errors.rb:3:in `with_friendly_errors'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/lib/ruby/gems/1.9.1/gems/bundler-1.3.2/bin/bundle:20:in `<top (required)>'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/bin/bundle:23:in `load'
	from /usr/local/opt/rbenv/versions/1.9.3-p385/bin/bundle:23:in `<main>'
````