[Gemfile] Improved detection of CocoaPods-version.yml path.
[Gemfile] Use the last known version of CocoaPods.
Prepare for 0.6.0
[Gemfile] require CocoaPods 0.6.0.rc2.
[Gemfile] Restored CocoaPods requirement to last known version
[Rakefile-Gemfile] Adapted for validation changes in 0.6.0rc1
Add rake to the Gemfile.
Add Gemfile and Travis config and make sending SIGINT during the lint…
… task work.