Merge -c 1523885 from trunk to branch-2 to fix HADOOP-9944. Fix RpcRequestHeaderProto.callId to be sint32 rather than uint32 since ipc.Client.CONNECTION_CONTEXT_CALL_ID is signed (i.e. -3). Contributed by Arun C. Murthy.

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Preparing for hadoop-2.1.1-beta release.

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Added ASL2 header to releasenotes.html.

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