Implemented update_mode == :selected
Ignore RVM files
Ignore Bundler temporary files
++cocoapods-integration-specs and mirror changes in spec/integration
Implemented integration test for update_selected
Changed spec as `pod update` falls back to `pod install` if no Lockfile is present

Because it improves the user convenience and bundler does it the same way.
Allow to specify which functional spec should be run by rake argument

e.g. rake 'spec:functional[command/project]'
The single quotes are needed for zsh.
Added a functional spec for telling the user that the Pods cannot be updated unless they are installed
Implemented check if all requested Pods are installed