Support for `header_dir` attr in subspecs.

Introduced Chameleon fixture.

The change is small refactoring to make clear which methods
return relative paths.

* master:
  List all the specifications of a local pod.
  Improve error message for missing local pod. Closes #323.

[Platform] Require a name on initialization

Closes #305.

* 'develop' of github.com:CocoaPods/CocoaPods:
  Rubinius on Travis does not seem to pickup the UTF8 default external encoding.
  No need to run `pod setup` manually. Closes #315.

Closes #304.

Switching to `json` because `ASIHTTPRequest` contains subspecs which are confusing for an illustrative purpose.