The caching of LocalPods might need a refactor.

Closes #485

See #485

Closes #484

Fixes: https://secure.travis-ci.org/#!/CocoaPods/CocoaPods/jobs/2236387

* pod_update: (37 commits)
  [Specification] Provide a meaningful error message if a subspec can't be found.
  Update lockfiles of examples.
  Handle pods in (case-insensitive) alphabetical order.
  [outdated] Don’t show pods that can't be checked.
  Fix outdated command.
  Improve Podfile.lock version when the `:head` option is used.
  Improve error message when a local source dir doesn't exist.
  Refactor and cleanup command source files.
  Don't break when a command isn't recognized and trying to show a help banner.
  Changelog.
  [Specs] Minor fix for Lockfile.
  [LocalSource] Specs.
  Changelog.
  Changelog.
  [Lockfile] Fix specs for grammar change.
  [Lockfile] Grammar.
  [LocalSource] Tuning.
  [Lockfile] Encode checksums only if supported.
  [ExternalSources] Better robustness :-)
  [Lockfile] Save checksums as string.
  ...

Conflicts:
	CHANGELOG.md
	Gemfile.lock

The output of this looks better.

* local_source:
  [LocalSource] Specs.
  [LocalSource] Tuning.
  [ExternalSources] Better robustness :-)
  [ExternalSources] Robustness.
  [LocalSource] Initial draft.

Conflicts:
	lib/cocoapods/installer.rb