Do not check Gemfile.lock into version control.

http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
Identify development dependencies.
Remove asset dependencies.

* Confirm that assets:precompile works on dummy app.
Merge pull request #1 from lovewithfood/identify_development_dependencies

Identify development dependencies.