Bug 935987 - Part 2: Add preprocessed files to mozpack.files; r=gps

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extra : rebase_source : fe32f92b22aecc82ea1b6d95a5ee43e274a9f8be
Bug 935987 - Part 3: Add preprocessed file support to install manifests; r=gps

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extra : rebase_source : a6897be53064bd171bd9280735c513c6ff539a4f