Fake vDSO is wrong for gettimeofday and friends

[stephenrkell]

We effectlvely take a snapshot of the kernel's page, which is wrong when the data might change. We need to divert references to our copy so that they point (cross-DSO) to the original vDSO data.

[stephenrkell]

I wrote a simple gettimeofday test case and was surprised to find that it works! So my understanding is out-of-whack here. First step is to check that it really is using vDSO shared memory to implement the call.