Fixes an issue where XCTest is missing in Xcode 6

The XCTest.framework bundle has changed location in Xcode 6. This PR
fixes this [#2296](https://github.com/CocoaPods/CocoaPods/issues/2296)

Conflicts:
	CHANGELOG.md
Bundle: update cocoapods-core

Required and update to the fixture spec repos
Merge pull request #2332 from lordkev/fix-xctest-xcode6

Fixes an issue where XCTest is missing in Xcode 6