Merge branch 'issue_1449_duplicate_prefix_header_contents' of https://github.com/luisdelarosa/CocoaPods into luisdelarosa-issue_1449_duplicate_prefix_header_contents

* 'issue_1449_duplicate_prefix_header_contents' of https://github.com/luisdelarosa/CocoaPods:
  Addressed comments from @irrationalfab: - simplified collection of unique prefix_header_contents - reduced sub specs in spec from 4 to 2 Removed inline documentation and added @notes and @todos. Added entry to Changelog.
  Fix issue #1449 by collecting the prefix_header_contents and uniq-ing them.
  Add integration test for issue #1449.
  Added two tests for issue #1449 - however both are passing at the unit level so I suspect that the issue will need to be tested at the integration test level.

Conflicts:
	CHANGELOG.md