messaging based counter for rerun

[satra]

we should determine whether the correct tasks are rerun using messaging.

if we write a message saying "Loading precomputed results", then we can count the number of such things for any graph and determine if the rerun was successful at only recomputing the necessary elements and also respecting graph hierarchy.

[djarecka]

once we have it, the tests "test_cachelocations" should be updated