Xcode 5 DP Support for JSON Compilation Database Reporter

With Xcode 5 Developer Preview, Apple has changed the intermediate pch generation from '.pch.pth' extension to '.pch.pch' instead. This pull request is to support both '.pch.pch' and '.pch.pth' extensions in JSON Compilation Database reporter, in order to accommodate Xcode 5 DP and Xcode 4 users.