allow disabling automatic full collection when computing growth

[71FIL]

I recently experienced a manifestation of https://bugs.python.org/issue39061 which I had worked around by running a full collection (gc.collect()) at regular intervals. I started using objgraph to try to find the source of the "leak" (the reference cycle) which moved and accumulated objects in the generation 2 collection which also made the issue disappear, just as my regular garbage collection was. I thus assumed that objgraph was calling gc.collect() and indeed it was.

I commented out the call to gc.collect() in growth which allowed me to identify the reference cycle which I could fix using weakrefs.

I would like to propose a new option to the growth/show_growth functions to disable the automatic full collection. Maybe running a generation 1 collection or none at all even if it means that there would be more false positive showing up in the growth report.

This is a proposition and I will gladly do the change if it sounds like it would be useful.

By the way, objgraph has helped me more than once at this point. Thank you very much.

[mgedmin]

Huh, that's an interesting use case.

I would accept such a PR.