Add _id to fixtures.
Pre-process data all the time.

Pre-processing data will make a few other functions simpler. Start by
updating getRelatives(). Since xhprof gives a fairly flattened list of
data, flattening it more won't really hurt.
Convert calculateExclusive to use new data structure.

The method is considerably simpler now that it isn't processing and
calculating at the same time. It also no longer destroys the original
data as it has already been transformed.
Update run.php to use new functions.