gistfile1.txt

$ ruby --version
ruby 1.8.7 (2012-02-08 patchlevel 358) [universal-darwin12.0]

$ bundle --version
Bundler version 1.2.3

$ cat Gemfile
source :rubygems

gem "curb", "~> 0.7.8"

$ bundle
Fetching gem metadata from http://rubygems.org/..
Enter your password to install the bundled RubyGems to your system: 
Installing curb (0.7.18) with native extensions 
Using bundler (1.2.3) 
Your bundle is complete! Use `bundle show [gemname]` to see where a bundled gem is installed.

$ cat Gemfile
source :rubygems

gem "curb", "0.7.12"

$ bundle install
Fetching gem metadata from http://rubygems.org/..
Installing curb (0.7.12) with native extensions 
Using bundler (1.2.3) 
Your bundle is complete! Use `bundle show [gemname]` to see where a bundled gem is installed.