New allocation profiler

[Vladimir Sitnikov]

>$churn accumulates the results within the iteration

As far as I can understand, installHooks is performed in
beforeIteration and it clears churn.

Suppose the following:

iteration 1 observes {PS Eden Space}.churn=10MiB
iteration 2 observes {PS Eden Space}.churn=0

What is the expected output?
I think current code will omit result from iteration2, thus it will
output "average=10MiB +- NaN", while it should result in something
like "average=5MiB +- 5MiB".

How is that supposed to work?

I think we'd better trim zero results right in the output, not during
collection.

Vladimir