Bug 1006812: Use mozilla::pkix::der to decode the key usage extension, r=keeler, a=sledru

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extra : rebase_source : 3ec7634564e0e87c4b45fb03f96c4984c68afa19
extra : histedit_source : 0f47e4a2d0333aafa7ec1f8f56011ef1cf474916
Bug 1031542: Add test case for key usage without any value bits, r=keeler, a=test-only

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extra : rebase_source : 29fac25dc419d6d9eb7acb0cbddd05e8a460f399
extra : source : 25bdc0db6b042fe6fbba61b80cb8a4ac7cb588eb
extra : histedit_source : a88d4395856723c73e2717909ae714bd2270ae0e