Bug 1098990 - Correctly parse version 1 trun segments where the composition time is signed. r=ajones

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extra : rebase_source : 4e7103f8a9bcd47a481c6db89366a09d033d1920
Bug 1100176 - Avoiding infinite loops when encountering a sidx box. r=ajones

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extra : rebase_source : 6f957d02ef1fb02a5ec446761e64e69b5922641c