Bug 898431: Update to NSS 3.15.4 beta 7 (NSS_3_15_4_BETA7), r=me

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extra : rebase_source : 51f5e01db5d8dec46f341e217fa2ba97382c723c
extra : amend_source : 04d8a9e4a861228c217b9d766cd8781d49ed496f